Hmmm, is this still being worked on? I think this is a very interesting project but there is 1 issue that will be annoying.
AI Seemingly only read Castle01, and will ignore 2 and above. Ignoring of course Tiny and Keep only castles this means that if we want AI to actually use any other castle, we would have to constantly rename Castle files to be used.
I find this odd as Stronghold 2 supports up to 4 AI castles per AI, so i don't know what Firefly changed, nor am i sure if it can be changed to allow more than 1 castle to be read.
Proper MP is one of the only things they actually mention in the trailer so you are covered on that. As for AI who knows.
Collisions i don't think would be possible since SH1 had no collision system at all, hell there was no collision system of any kind in these games unti like, well Warlords.
You can already cap abandoned siege machines and any unit can already take over gatehouses, i mean its what siege tower is for, to allow you to acomplish that.
Knights and Siege engines can already walk on walls if they are on same height plane [although i think this is just a bug rather than something intended, but it can happen]
We already have different towers... I really don't get some of you points since they are already in the game.