One of the things I like in Capture One is its ability to show what area of the picture is in focus. This is done simply with an edge detection and shown with a green overlay. Tolerance can be adjusted. There are even cameras that do this.
It's a very nice tool to have when sorting though piles of photos, especially sports, birds and generally stuff where not all pictures will be in focus. Rather than zoom each image individually to 100%, the tool would show instantly if there is a focus issue - out of focus, backfocus, frontfocus.
As a bonus (though maybe not in Lr4 but in a future version), Lr could filter images based on focus.
This forum is primarily focused on the new features and bugs in the beta release, so it'll be closed when the beta finishes. The best place to get your requests considered is the Feature Request forum http://feedback.photoshop.com/photoshop_family because others can also add their votes so Adobe can see which requests are most popular, and the requests can be easily tracked. They stand a much better chance of getting attention there too. I think there's already a request over there, if you do a quick search, so you might like to add your vote.