> Would you pay for source-available products? GPL and paid license?

I'm not GP but I would at least consider it. I say that as someone who refuses to build on closed-source tooling or libraries. I'd even consider closed-source if there was an irrevocable guarantee that the source would be released in its entirety (with a favorable open source license) if the license/pricing terms ever changed or the company ceased to exist or stopped supporting that product.

> Along with a guarantee that you get to keep access to older versions (Jetbrains and Sublime Text models)?

I like that for personal tools but I wouldn't build my products or business on top of those. I've had too much trouble getting old binaries to work on new OS versions to consider these binaries to be usable in the long term.