It seems to me that the basic issue with nokia is that they see each generation as a platform, much like a phone (oddly enough), and that they as a company have not grasped the concept of hardware and OS as being seperate entities, otherwise we would have had Maemo 4, and then 5 as an OS which would be installable on the different hardware platforms, much like general Linux is.
Also I agree with whoever said that Nokia need to move away from huge update releases to much smaller updates for individual modules and release them as they are available. Everyone else including MS do it.
Mer was a massive job for the community to pull off, and it seems to me like they nearly managed it, but the enormity of the task for the very limited resources meant that in the end it was too much. Lack of resource is publicly why Nokia have stopped building "Hacker Editions", so it's hard to see why a handful of dedicated volunteers working in their free time can pull it off.