Interesting idea about making image proxy a per feed setting. From my limited experience it works well, however some some sites may block it. Maybe I will implement it.
Regarding per feed full-text. I’ve had a plan to do it for a long time. Without changing feed URL, making full-text feed core feature. But there are always some other features to do and I’m not sure whether blog authors will like it so I’ve decided to self host Five Filters service as at least something before bright future come true So yes, I have a plan for it.
Collapsing overlong tag lists is a good idea. But can’t say when I get to it.