According to the lastest dev blog on update 2 the new features look great. As well as usual balancing there's some big changes to things like heroism, a whole new decision-style system and the release of the assembly kit!
https://www.totalwar.com/blog/allegiance-update-beta-2
Taken from the above link:
Today the second version of the Allegiance beta is now available, which includes changes made as a result of feedback gained on the first beta as well as introducing other additions and changes to the game we have wanted to make. The big new addition is Decrees, a version of the Rites system from Total War: WARHAMMER II that allows players to make a choice to spend something in return for a bonus for a number of turns. We’ve also made large changes to mechanics like Heroism, Legitimacy, Tribute, Here King and introduced a new mechanic called the Burghal system for the English Kingdoms.
EDIT:
Seems like only Dave and BoB are working for me, Terry, Ted and the variant editor all throw errors that seem to mention Attila. Do we need Attila installed for those tools to work or something?