While I understand that syncing to the past is 'iffy' and weird stuff can happen, I thought it was odd that when I spawned two clients at different times, one could sync to the future, but the other couldn't sync to the past:

I disabled that when I changed the historic update grouping from subspaces to individual vessels. If this is re-enabled, players will still not be able to send updates for vessels manipulated in the future.

It gets a bit iffy when you do things in the past with a vessel after you do something in the future with it ;)

Ah ok. I don't particularly plan on using it a lot, but it might be nice if you accidentally do something silly like warp several years into the future.

I think it might be worth considering adding an option where, when you click 'sync' on a past update, it pops up a dialogue box saying "Syncing to the past will delete all vessel updates after the point you are reverting to; Be aware that weirdness may occur".

What about a function that returns a bool if the player is in the past/present/future?
Then, just toggle no-clipping on past users.

Err, not sure a bool would work for 3 states :P
But in any case what you're explaining is starting to sound a bit like my suggestion #80 however I think darklight's point was that all events saved for your vessel in the future would become invalid if you warp to the past.

I think if we do enable syncing to the past - It should only be done while we aren't in flight, and we shouldn't let players do a double burn, aka: The vessel has been changed in the future" should also work for your own updates.

We'll keep the time-paradox talk in #80 - That is going to be a hard bug to solve.

Closing this one - There's way too many things that can go wrong with syncing to the past :(

Agreed. I only mentioned it since it was possible at one point, but the paradoxes and weirdness are not worth it.