My biggest wish for Reaper 5 is that it contains some really big changes.
All the little changes can stay in 4.xx but Reaper 5 will require a Reaper 5 Explained tutorial (shameless and selfish) and I don't want to do it for small changes.
I'd like:
1. VCAs
2. Area Selection and Editing
3. Elastic Audio
4. Playlist type Editing and Comping
5. Edit Groups
6. Bundled Virtual Instrument Plugins and Sounds