MeeGo Touch is the ui library (add-on over plain Qt). The "user interface" consists of lots of stuff in addition to that, including app launcher, homescreen, system status bars etc.

If you need to develop applications, you need the UI library. You probably won't need the homescreen or app launcher. Don't count on all of this being made available.

If you asked me, you don't need to wait for this release to develop applications. You can already develop meegotouch applications for your current N900, without flashing it. You could also distribute those apps to current "mainstream" n900 users.