For me the support that Nokia provided in the past was fine for the products I own/owned (all the Maemo devices and a number of Symbian phones). In my opinion, better than the support Samsung or HTC provide.
I trust that Nokia will support the N9 in a similar way, so that will be fine for me also. When I buy the device, I will do so for what it can do at that moment in time, and not for any future promised updates.
When it is released, I will probably buy it if it isn't too buggy, the basic applications aren't too dumbed down, and the device isn't too expensive.
Otherwise I will wait a bit longer, as my N900 devices work fine, and I don't "need" a new device. Prices will come down, alternative applications will get released, and bugs will be fixed.
In the end I think I will end-up with a N9, as I don't feel other devices will provide the features I want.

I think the N9 will be similarly supported as the N900, and I think the N9 will be the only MeeGo device that a relatively large group of people will use. I don't believe the MeeGo builds on the MeeGo website will ever be used on any large scale, simply because I don't think it will ever get finished to an end-user state, by anyone.

So far for my two cents
I have been known to be wrong in the past (on many occasions actually).