I am probably not the first to mention this, but what about a Harmattan-UI mockup for the CSSU? I know that lots are not a fan of it, but it would be cool to replicate this and would make a good addition IMO. For example:

- The application launcher would not be too much trouble if you keep 3 rows (instead of 4) and use the existing s-anna icon pack with CSSU-enabled portrait mode in this menu.

- The task switcher is already there, and with forced autorotation (CSSU-enabled) it will work and look almoast the same as with the Harmattan UI. Under medium to high load I find the task switcher sometimes reverting to landscape unwillingly, I am not sure if improvements on this can be viable for the effort.

- The notifications screen would be troublesome to create, but not impossible. It coule be an app showing the latest updates like missed calls, conversations etc. but this would be pretty versitile. An other way around could be to create some kind of QBW instance (possibly in portrait by default) wich shows this kind of information, but then you would see hildon-desktop and you might wanna revamp it so it looks better in portrait. In this case you might only want one homescreen.
Or you could scrap this part, since most notifications show up in the dashboard along with the running apps.

- the swipy gestures to achieve this along with the effects could be a headache too, but it doesen't seem impossible. Of course, the rest of Maemo5 should not be sacrificed for this and could work as an alternative way to navigate through the N900.

What do you think?

regards