I would have to think two-way CC support is one of the first major things they would roll out. But I hope they don't stick to strictly TV like features.
I think Tivo has to realize that if they are going to appeal to the average user as a $300 replacement to their cable provided DVR, that they have to branch more into streaming media. Their main competition in the future has to come from the $150 streaming boxes like the Roku, Boxee, and Popcorn Hour.
I'd love to see them add local LAN (SMB/CIFS) streaming of MPEG4 media as well premium partnerships with the major networks. The Youtube thing is nice when you want to find a quick clip but the quality is awful and the Netflix interface is horribly and slow. I typically use my 360 for Netflix content. So of course, as everyone mentioned, a speedier/redesigned UI would be nice too.
I love my two Tivo's and have lifetime but if I can get the all the content from some other internet source without cable, I would have to drop them. This is why I hope they smell the coffee and bolster their streaming efforts more. We'll find out tonight.