Well, to start speculating, might as well and attempt a recap of what we know? I will start a list, if anything is missing, please copy paste and add to the end :3
1) Two battle scenes are done, and two cities (for all that we have been shown°
2) In battle, formations are a big deal. Leaving behind our simplistic interface, Bannerlord replaces it with one offering more depth. However, it seems easy to grasp as well.
3) Horse animations are fantastic.
4) According to my understanding of the videos, Cities are divided by who owns the castle, and who owns the streets.
4.1) This means that you can destroy gangs in the streets, and put your own men to replace them. I think that if you do so in your Castle, that improves the city overall, but if you do it in someone else's, you have the choice to become a thorn in their side.
4.2) On that same note, the cities feel more alive than ever, but what about actual castles? Hypothesis suggests that it would look either like a compact city, or training ground for soldiers.
5) You can craft weapons, but no bows or armours.
6) There seems to be an evident "Bad guy" or "Boss" with the Vladians (Swadia?) It appears to have the biggest empire from the get go and the most heavy troops.
7) We have seasons, the economical impact is yet to be seen. Same for the impact on waging a winter war (freezing soldiers, food supplies drop faster?)
8.) We have a story mode, but how different will it be from the one we know from Vikings? Will we have more freedom? Will it be more similar to Fire and sword, where we get killed if we win?
9) The battles seem for now to support more than 160 units per side. Not bad at all, but since the maps are bigger.... Is that the cap? Or could a monster PC handle 1000 units? Or even 500? WIll it lag out like in Vikings?
10) We can upgrade our villages. Can we do the same with our towns?
11) We have apparently access to siege equipment. However, if today most of us could figure out how to build a rudimentary catapult, will some less knowledgeable factions have a limitation to what equipment can be fielded?
12) I might have missed the descendants part, but I thought that was just speculation. Please confirm dear reader.
13) The trading and bargaining system is supposed to have received and overhaul. We can trade for peace, soldiers; prisoners, what else?
14) Mods will be core to the game. Will we see a COOP mod? Is COOP the big surprise? Like a constant party of two heroes?
15) To be added
I am sure I missed a ton of things, but perhaps you can add; or start discussing once more (because in 2000+ pages I'm sure most of this has been discussed) about some of these.
At any rate, hope this helps any new comers.