The ideas are mixed up from suggestion at github/forum from users, CJ and mine. The idea is based on the fact that the tunnel bore was created long time ago and even before the first locomotive.

General Ideas:
I would love to see an redesign of the tunnel bore model. I think it's really easy to understand why:

• you can't see whats ahead when the tunnel bore stops (maybe the front should be a hexagon)
  • or a vanilla/RC design that fits
  • better fitting collision model would be great so you can walk in a 3x3 hole aside the tunnel bore
  • 2nd idea: if the bore head were removed the model will change into a smaller one (so you can see whats ahead)
• the skin and the model are a little bit outdated -> if you look how the locomotives are designed you see what I mean
• energy as a fuel

Bore heads:

• enchantments:
  • unbreaking
  • Efficiency (it will increase the speed up to 40% but also increase the consumption of the fuel)
  • Silk Touch

Tunnel Bore Machine
features:

• new movements:
  • move backwards (only slow)
  • bore mode (only forwards - active/deactive mode)
  • following tracks (can go into a turn)
  • can step up/down 1 block
• can be filled with the itemloader

Advanced Tunnel Bore Machine
features:

• same as the normal one (new features included - above)
• includes an under/over/side cutter
  • that means a tunnel across the ocean is possible
• instead of fill low spots it got an option to
  • build bridges
  • fill holes
• can set torches

That's what I think and I would like to discuss with all of you my ideas (open for suggestions).
Maybe we have to split the ideas (model/bore head/tunnel bore). We will see how the discussion will start.
The new recipes should not be the problem. I already got some ideas and I think it should 3 time more expensive than the normal tunnel bore.

Personally I would also like to have a seat at the tunnel bore. But thats only a dream^^
So we have to find a solution that perfectly fits in the RC universe.

Ps: I don't think I have to say that I love to create new tunnels ^^

I would like to keep an element of player interaction required to operate the Bore. As such you'll probably not be ever able to automate it 100%. I also would like to keep it at a fairly accurate analog to real life machines.

Things I would like do to with the Bore:

• Bring fuel design into line with the Locomotives: Steam/Electric
• Make a 5x5 variant that can line the walls.
• Torch support.
• Split into a multiparty entity (like the dragon) to fix collision issues.

Things that would be nice but that would be a real pain to implement:

• Ability to step up/down at set intervals. Logic is horribly complex and the model will have clipping issues while doing so.

Things that don't fit the theme/reality/limitations and probably not happen:

• Bridge building, there are machines in real life that build bridges, they are not tunnel bores.
• Tunneling through water, doesn't make sense compared to real life and mechanically water is a pain and likes to wash away tracks.
• Turns, allowing the Bore to turn makes the code much more unreliable and complex. Also clipping.

Things that already work:

• Item Loading should already work.
• Enchanting Bore Heads (just durability, but would probably not be hard to add more support)

EnviroMine support:

• Hmm... This would be nice, not sure best way to do it while maintaining realism. I'd have to put the lining in place before mining the tunnel, which is kind of weird. I'm not totally against this, it's just weird and I'm open to suggestions.

Also, thanks @Suterusu1337

I recently added enviromine into a pack with railcraft. When I did this, I noticed the TBM from RC became useless because of the constant cave-ins associated with enviromine.

Real life TBM will place concrete "pads" along the tunnel wall as it bores. These concrete tunnel wall sections build the actual outer tunnel and shield the TBM from any cave-ins.

http://www.railway-technology.com/contractor_images/larsen/2-tbm-tunnel.jpg

It would be neat (and practical, really) if the TBM was able to replace wall sections with concrete...

Example 1: Dig a 5x5 and replace the wall sections with concrete blocks from the linked carts forming a final 3x3 tunnel.

Example 2: Replace "loose" material (sand, gravel, dirt, configurable) with concrete blocks in the 3x3 tunnel leaving ores, stone, etc.

As is, the TBM will dig forward through dirt until the dirt falls on it (the TBM obviously isn't holding up the tunnel)

http://www.discovery.com/tv-shows/other-shows/videos/mega-engineering-tunnel-boring-machines/

Here's a longer one about the same project if you have 45 minutes to spare
https://www.youtube.com/watch?v=QaTN_R1b00I

General idea sounds great!
I have also trouble when tunnel bore stuck and i cannot see why but i think your solution will not work. I.e. in nether often there are blocks of lava, and even if you could see though tunnel bore you would not see lava, because of one block thick netherrack. In my opinion better solution is removable bore head from model of tunnel bore. Machine would get smaller, you can fit between her and side wall and manually investigate.

Bridges or something similar is needed, but this is dangerous conception. It could lead to an abuse. It could be too powerful. Personally i would like config to set how big gaps should be filled with gravel (so it don't use up entire gravel on one big cavern) and maybe config to build bridges but rather small, few block across.

Other ideas sound great to me ;)

I like your idea about the removable bore head so the model will change into a smaller one 👍
For me it is a mess that I can't build tunnels in the ocean.
The only actual solution is to dig a hole down (because the tunnel bore can't get up/down - and can't follow tracks up/down/turns), place tracks and set the tunnel bore again. It's a very hard workaround^^

So a button in the GUI for fill holes/set bridge could be a solution. I would help to develop an easy GUI interface.

What if advanced tunnel bore dig 5x5 tunnel? Then easily bore head can be 5x5, but core part 3x3 (or 4 high), so one block would be free space on both sides.

The idea sounds good. But what if the bore head is indicator for the size of the hole?
So there are 5x5 and 3x3 bore heads.
But the actual problem that you can't go at the side of the tunnel bore with a 3x3 head would be the same. Also that you can't see what's ahead.
So I think we need an redesign of the model. A little more curves at the head (I know it's not vanilla design style)

you can't see whats ahead when the tunnel bore stops

Tunnel Bores are massive, even without the bore head, them blocking the sight is actually pretty cool, in my opinion. Solution: just dig around the bore to see what's in front of it, it's really not that hard and actually is pretty close to how real Tunnel Bore issues have to be fixed.

Building Bridges doesn't make sense to me, that shouldn't be a thing as it's a very nice mechanic to have to fill holes with gravel or crushed obsidian (building floating bridges would be like having Suspended Tracks with no limit). The bore automagically placing down torches makes no sense either.

Tunnel Bores are massive, even without the bore head, them blocking the sight is actually pretty cool, in my opinion. Solution: just dig around the bore to see what's in front of it, it's really not that hard and actually is pretty close to how real Tunnel Bore issues have to be fixed.

The question is should it be real or should it be MC/RC style?

Building Bridges doesn't make sense to me

It's not actually only building bridges. It's only a side effect of building tunnels in the ocean.
In my opinion it's needed if the bore can't step up/down.

Alternatively tunnel bore could be in modules, each 3x3x1 blocks. When digging up/down, every slice of the machine could be moved by an offset +/-1 vertically.

One feature I want to see the most from this list is torch placement, I'd advise on the middle of both sides of the tunnel every 4th block length-wise. I like to ride along with my TBM as it tunnels and I have to place the torches manually which becomes daunting after a while. RL TBM's lay their own concrete tunnels so I don't see why placing a torch is such a stretch.

If realism is a concern for torch placement, you could make it drop a line of glowstone instead.

@CovertJaguar This is one of the major features that hasn't been assigned a milestone yet. What are your thoughts?

Also, enchantment support was added by #1135, which also handles Fortune.

I'll assign it to 10.2 for now to co-incide with #423

Eh...that's probably super optimistic. I really don't see myself revisiting this before 10.4 or 10.5 at the earliest.

Another change that would be simple to implement - allow inactive bore to be pushed by a locomotive. Or better, give it locomotive's mechanics.
As for walls reinforcing - IMO it should be done by separate cart, much like undercutter.