I think with VST3 there’s no way to configure additional folders to be scanned by Cubase. Which is too bad, because my VST3 folder is getting to be a bit large, and it would be nice if I could break it into several folders.
The reason for that is, that I also use other hosts (e.g. Unify, Bidule, Komplete Kontrol, Maschine), and I’d like to more control over what plugins are available to each host. With Cubase at least the Plugin Manager allows me to make my own collections, so that’s generally good enough for me inside Cubase. But not all hosts have that kind of “collections” ability. And of course it would be nicer at startup time to not bother scanning things that I don’t want a host to use.
I do however empathize with some of these types of Steinberg decisions, because they make things more foolproof for nubees. It’s us advanced/ambitious tinkerers, where some of these hard coded things don’t allow for the flexibility we seek. So this is not even something I’d raise as a feature request.
For a software (or hardware) provider it’s very diificult to make things ultra flexible without having lots of users shoot themselves in the foot. And when that happens, the software supplier typically gets blamed for it, regardless how unfair that might be.