At the moment, the "web 2.0" bandwagon is rolling fast, and the multifunctional forum will be subsumed into the awful biomass that sits like a smog over the web.
However, just as the forum never made usenet redundant (though arguably it is not what it once was*), so web 2.0 will not remove the specialist forums - indeed, quality forums may gain as refugees from clone-land seek a safe haven ;)
I don't argue with any of your suggestions, I just hope we continue to have a choice, and once the current bandwagon overturns, the best will remain.
I come here to exchange info on SEO; I don't want a date, I don't want to play ScrofulousTM (or any other gizmo).
I don't want the ego-boost that blogs give, or the disjointed exchange that follows among the 'followers'. When I want a blog, I go to the individual's own blog, not a marketplace of people vying for attention and praying (in vain) for SEO benefit.
I suspect I'm not alone :)
Don't forget that there are already waaay too many blogs. I'd guess that blogs outnumber readers at least 10 to 1 - and most blogs have virtually no readers at all.
There are too many forums, too. But forums can serve small niches, and some specialist ones do well on a handful of members.
web 2.0 however
1. REQUIRES many readers for the format to work
2. Will be dominated by a handful of sites:
I can successfully have a list of 20 blogs via RSS; I can visit 20 forums as the mood takes. I cannot have active (useful) membership of 20 web 2.0 sites and still get some sleep.
*People always say that usenet isn't what it once was, to which the response should be "what is?"