I must admit I'm a bit confused on the meaning of "support" / "community support" here. I find it hard to believe that Harmattan firmware will ship without GTK+ & Hildon. For one thing that would mean Nokia would have to rewrite every GUI app/component from scratch, including some decidedly non-trivial ones like modest and microb. For another, installation of practically any pre-existing third-party app would pull in the GTK+ stack as dependencies, so it might as well be preinstalled.

On the other hand, if GTK+/Hildon are part of the official firmware how would the community be able to support (publish updates and so on) them?

Some clarification would be very welcome please.

Sure, Qt is even available for Diablo. That's fine (although having two large-ish GUI runtimes in RAM seems wasteful), it's the dropping of GTK+/Hildon support part that's surprising.