Considering the number of devices that Nokia make, plans being made are always about the future. Whatever work they do for the current existing devices is support. Bugfixing, or bringing functionality that marketing already promised but they failed to deliver on time.

Maemo can be said to be different in that respect. Because it's this much of an open platform, all the work they do for the M6 generation of devices may (or may not) be easily backported. If they want a blooming community around Maemo, they will be willing to put in some extra effort in backporting.