"How would this be different from previous Golos and Whaleshares forks?"

This would be a much larger migration of devs, stakeholders, and apps running on the chain. It's also not fundamentally changing the code or being run by incompetent people. The resources would be much greater than either of those "forks."

"Who would be the buyers of the new STEEM and what exchanges would be available to buy it on?"

Anyone who wants to buy into the community, I imagine, would be buyers. The token would be available on whatever exchanges list it. The same way Steem started, but this time, having an established community is an advantage.

"Also, for existing dapps, would they be able to run on the forked chain?"

Yes.

"What would it take for them to migrate?"

Pretty much just a name change, if needed.

"I'm not clear what it was, but isn't it still going to be needed? Who will pay for that and maintain it?"

Yes, and it can be funded via witness rewards or the SPS, or even self-funded. Donations could work as well.