Thought of a few more things besides the return of titles...

1. I'm going to assume most of the playable factions will still be governed by a monarchic form of goverment...so I hope CA brings back the option to change your faction heir.

2. Making alliances actually worth something. Have an diplo-option similar to Europa Universalis wherein if you go to war, your ally(-ies) immediately must choose to honor your alliance and fight alongside you (or subsequently back out and lose a tremendous amount of respect). Likewise, if your ally goes to war with faction neutral to you, you have the option to support your ally or take a big hit against your reputation/prestige by stiffing them.

I've always dreamed of seeing campaign battles with one or more allies fighting along side you against one of more opponents. Have never come close to seeing that happen in any campaign going all the way back to MTW.

Implementing multi-faction battles would truly make alliances so much more worthwhile and the battles themsselves so much more epic.