Perfect/fully working UI for meego isn't needed on n900.. What's very important is for the UI to be implemented enough to use the core OS of meego for it's phone functionality. Maemo's UI is good enough already and suit the n900's design. Remember what most users aim for meego is the OS's additional functionality which focus more on the device's telephony module like T9 keyboard, 3g video calling, portrait mode GUI & many more(I mean very2x many). You would know if you would read all the replies of members waiting for the official meego release or ask them what they aim at the meego platform.

So a wild guess... Upon alpha release of the meego OS w/ initial UX on june. Probably most n900 users would prefer to dual boot it already just for the sake of the maemo 5's lack of features. That is if the alpha version would be enough to make the said features work at least slightly stable.