So, putting legal solutions aside, there could also be a technical way to solve this: a company with a VST2 licence could offer a very simple VST2/3 bridge plugin.
I have not touched the hosting side of plugin development yet so I have no idea how hard it would be to do this, but at least this is doable as Blue Cat’s PatchWork does it (among many other functionalities).
Companies not having a VST2 licence could then advertise their plugin as VST-compatible when used with this particular bridge, with a link to that company’s website.
To be a viable solution it would have to be free, but that would be a good investment for the company offering it both in terms of web traffic to its shop and in terms of reputation.