There are a few things i would really like to see in TA.
For starters, when i get attacked i dont want my allies to jump in already, if its a small enemy i want those planets for myself. However i would like an option in the diplomatic screen to request backup while the war has already begun. At that point they have the option to either obey or break the alliance.
Same goes for the IA, they wont request my help untill they feel its needed.
Maybe some more options on how to help an ally.
So that you dont have to declare war on a certain clan just to help your ally, but maybe give them a certain % of your income to help (like 10% or so?). Kinda like a third treaty that only allies can have.