Ability to link to images in chat that are stored on our forum, rather than images on the internet.
Ability to invite people into Chat from the forum, inside the chat room
Ability to have private chat with multiple users.
IPB is not bad at all on the resources, which also depends on number of add ons... however after year of phpbb on a shared provider, switched to IPB and was much faster... then as forum grew... switched to VPS, and kept upgrading, and now working on getting everything over to a dedicated.
As far as hosts... depends on who and how oversold they are. I have one vps that I kept as a backup, however it is slower than my first shared hosting provider.
If you have a weak site, with weak content, niche, sense of community, yes, your forum may be dead.
I think Facebook and other social media sites are just going to accelerate the weak players from the strong players. Unless facebook makes their own forum software, it is not going to happen. Just like email did not kill the paper industry, neither is facebook going to. In fact, learn to embrace facebook to drive traffic to your forum community, don't be afraid of your people leaving to go to facebook.