That's the problem. Massive changes between versions rarely work out. Think of something like Windows XP to Vista and you get an idea of the pitfalls.

Instead Nokia should be looking at the Android model. Sure Android has its problems but there's no shame in copying what works. Make small incremental releases which work on the previous device. Make a Maemo release every three months with 25% of what you want instead of one release in a year with 100% of what you want. With the latter approach I guarantee the following:

-It won't be 100%, it'll be 80%. Scaled back to meet deadlines.

-It'll still be late anyway.

-That 80% won't be what people want so you end with with maybe 50% of stuff people want in addition to missing the things people do want.

It'll also keep N900 sales strong since customers will be confident that the device is beign supported and it's getting new features all the time.

Will Nokia do this? Probably not, it's too alien to their thought processes.