Eventually, it will be interesting to see what functionality people have gotten used to in the current version of Basecamp that doesn't make it over to the next version and how those changes get implemented.

People don't always use tools the way they were intended to be used. Because of that, there are non-obvious features/functionality that may not have even been on the drawing board for the next version. Will 37signals go back and re-implement those subtle pieces or will they put a stake in the ground and say "this is the new way forward".

It could end up becoming an interesting study on how to bridge the gap with two systems when the next version is a complete rewrite.