I'm in two minds about this. (Ok, three minds if you're pedantic)
Autodesk already own Green Building Studio - another environmental analysis program. Why do they need another one? I would assume in order to reduce the number of competing programs - take over anything that might challenge them in the future.
It is a very shrewd move as environmental analysis will become very important for all new construction in the next few years. Becoming the main developer should be very lucrative. Why GS/Nemetschek didn't offer some sort of 'financial support' earlier, who knows? It would have been quite useful to have this type of software in their portfolio or even incorporated into ArchiCAD directly. I remember a press release from a few years back saying how well Ecotect works with ArchiCAD, so there was clearly some kind of 'relationship' which should have been leveraged.
On the otherhand, it is good news in as much as something may actually get released fairly regularly that works well, as I guess it was pretty much a one-man-band developing it before. (How long has version 5.60 been promised for!?)
I would also assume there will be some kind of consolidation of the features to some extent. They wouldn't develop two competing programs simultaneously (Well, maybe if they were Nemetschek with the Vectorworks/ArchiCAD weirdness!? but I digress! )
I can't help feeling this was a lost opportunity for GS, but I suppose we should just wait and see what Autodesk does with it in the future now it has some real backing. It may have been the best thing for it in the long run!