In server plugins, it would be very nice if we could have more control over data types management (create, modify, delete), or at least to get the list of types. And I hope that looping through lists will be allowed, since right now we have to solve this kind of problems with GUI/UX trade-offs.
Another new year’s wish is to build plugins that are containers (groups). Right now you cannot develop a plugin which could incorporate other widgets. Something like element templates, maybe (as discussed here)