The only thing that makes the N900 a "developer" phone is, well, nothing. It's a not-quite-consumer-ready phone that appeals to *nix geeks. If Nokia makes the "secure mode" thing a simple switch you can turn off, then there's no issue.

It should be completely transparent to the mainstream user. For Nokia, however, MeeGo is a decrease in developmental expenses that directly reduces costs, at the expense of someone's time to keep the device drivers current with whatever kernel/X release is in MeeGo at the time, and that's not much.

I don't think so, but considering that the entire OS is a downstream assembly from numerous independent projects MeeGo is in a far better position than Maemo ever was.

I have seen more than a few people working on Hildon Desktop and Modest in the past couple months, but the lack of effort in this area can be directly attributed to Nokia's weird behavior towards the community.

We can't do anything about closed bits. Ironically, the only closed bit I can think of that -directly- impacts performance is microB. Everything else is poorly tuned open programs (iirc) doing things at inopportune times.