What is happening here isn't merging. Merging is Nokia marketing speak for the death of Linux Distribution they created. Put is simple terms, Nokia is ditching their own home grown distribution (Meamo) in favour of Intels Molbin. They are porting their Qt UI libraries and a few apps, but that is about it.
Maybe some of the reasons for this were revealed in this post:
Any death causes a lot of angst amongst those who were close to the deceased, and this is no exception. The points that came up on most on talk.maemo.org, were:
1. Will MeeGo run on the N900?
2. What will happen to to the maemo.org community? (Good question, as Nokia hasn't said. But would have to think it will be the same as meamo: what doesn't migrate over to Molbin will die.)
3. Dislike of the move from a Debian based system to Fedora.
The last question was the cause of most consternation, and probably for good reason. It seems likely Nokia will do their best to make the maemo.org community feel at home at MeeGo, and of course MeeGo will run on the N900. But Debian packaging is dead, primarily because RedHat managed to make rpm the preferred format for LSB. That means all the packaging work done by the maemo.org community is also now dead. It also means Debian's package repository, which is the largest on the planet, will be lost to the community. This is doubly sad because Debian has an official armel port and Fedora doesn't, and many of the current Debian ARM binary packages just worked on the N900.
In the end all this probably means very little to Nokia. They had a go at creating their own distribution. It failed, and so they are making a commercial decision to move on. The users at maemo.org represent very little in the way of sales, the users they will loose because the N900 was a phone running mini Debian distribution are vanishingly small. But many in the community at maemo.org has invested something worth more to them than money, and seeing this investment sacrificed on the hard alter of commercial reality is proving a bit hard to take right now.