Things I'd like to see in LR4:
1. Book layouts. I absolutely hate having to maintain a copy of Aperture just to use its book feature. Give us the ability to lay out multi-page book spreads and export as PDF, and I'd be thrilled. Perhaps a partnership with one of the online photo book companies, too, to facilitate one-click printing a la Apple.
2. Layers. This one won't happen, since it would cannibalize sales of Photoshop, but it would be oh so nice to have the ability to make adjustments in layers, with proper masking.
3. Ability to invert, copy, and paste adjustment brushes. I often find myself using local adjustment brushes to do one thing (increasing local sharpness or brightness, for instance), and then wanting to make the reciprocal adjustment to the rest of the photo. This currently requires me to create an entirely new adjustment brush and paint in the changes. But what if I could simply copy the mask created by the first brush, paste it to the second brush, invert it, and then simply dial in my settings. This would streamline things greatly for me.