You suggested recently in your comments that you might be interested in suggestions for the mod.
I have a couple, and thought I would share:

1) A config value for the size of the area affected by each of the Hourglass block and the Activate block would be pretty cool. 100 blocks in all directions requires keeping puzzles quite distant from one another.

2)An In-Mod "Slippery" block that affects the pushable blocks in the way you've made Ice/Packed Ice affect them. Using vanilla ice is suitable for adventure mode, but an in-mod unbreakable option would be nice in survival applications, to prevent players from breaking/cheesing puzzles.

3) A config whitelist for more slippery blocks. It might be cool to be able to use Chisel's Ice Variants, or other arbitrary blocks, for aesthetics.

Thanks for having a look.

FYI, I forked this and plan to work on my own version eventually. However, even once I actually start writing some mod code, this is currently last in a rather long list of projects, so it will take quite a while before I do anything.

My initial focus (once I'm working on this) will be porting to 1.15 or 1.16, so 1) and 2) will be put off for later, however I'm planning to cover 3) in the process by pulling from the zblock:slippery tag.