It's not about how many plugins are in plugins folder. You can easily have several plugin collections there with over 100 rbx files. Also it doesn't depend much on how much plugin functions you use.
It all depends on how many entries in the global plugin function list are used by some plugin. I'm not sure how it's counted, but it seems like classes and methods certainly are added there. And this list has a limit, maybe those 8192 entries listed in the feedback case.
You can trigger it easily with this sample code in a new project.
Warning! This can crash Real Studio, so close other projects!
This triggers inclusion of enough plugin features so that the linker fails. Those classes reference a lot of other classes, so on the end, the list is full.
dim d as new DynaPDFMBS
dim c as new CDBarLayerMBS
dim q as new QTKitMovieMBS
dim f as new CIFilterMBS(0)
dim w as new WebDocumentRepresentationMBS
The only thing I can do is to split plugins into smaller pieces. But for that I'd need to know what people use and what not. And some plugin parts can't be split like ChartDirector.