Since everyone's making their predictions, here's my equally pointless analysis:

First off, lessons learned:
Tapping into the Open Source ecosystem is one of the major goals for the NIT project. So killing support on the n770 so early was something of a misstep, since the time frame was insufficient for all those projects to emerge. Also, part of sound marketing on a new product release is reassuring those who own the old product of the quality of their purchase. That's basic. So I don't see them killing support for the n800 right away.
That said, something needs to be done about the n800's video speed. Screen tearing on scrolling is a serious problem.
Likewise, if they're going to have a camera on a device, they better support it.

Now, as for what _did_ get developed for the NITs:
so far, the #1 breakout application is MaemoMapper. The really cool part isn't the Navigation feature (that's done better elsewhere), but the ability (as an OSS project) to gain access to extremely high quality maps and photographs (and in the future, internet POI databases), and present them in a device you can have in your pocket. Any number of navigation devices can tell you how to get from point A to B, but how many can deliver high-resolution satellite imagery of your location?

So it's no surprise that Nokia would be developing a tablet with built-in GPS. That's one of the most active areas for open-source development, and provides one of the most unique features.

the other big usage coming up is mobile VoIP. Skype-enabled WiFi phones are a surprisingly growing sector of the market, and a NIT's cost is close enough for people to consider them. Adding slide-out thumbboard? I dunno, if it works, okay.

The final element they should be looking to add is excitement. OSS projects aren't terribly good at this, but even so, many of the most involved OS projects are to make the media players look and work in a useful manner.

As for MOSH, heh. Everyone's looking for the next ITMS, where a hardware company used their market dominance to build an internet service. Good luck on that guys.