Yeah I'm hoping R20 brings the long awaited core update we've all been waiting for. I know we've got bits and pieces of it with Voronoi fracture, but hoping the new core gives us a more responsive viewport with more objects in the scene.
It would also be nice if we didn't have to worry about priority anymore. Dealing with laggy animations can be frustrating.
Improved boolean operations yielding better topology would also be lovely.
Last, and certainly not least, as others have said... we really need an updated UV toolset.
I'd be very surprised if all this came with R20, but if it did, I'd be in heaven