Hey Rory, you rocked it, thank you ! All good now, export as VST works as advertised, I'm a happy Cabbage camper again. Btw, I exported the waveguide1 processor, it loads and apparently works well in the VCV Host FX module. I'll let you know if I run into any really horrible problems.
Meanwhile, yeh, I don't know how much work you want to put into the Export As VCV Rack Module. It's a great idea, but if Rack's VST hosting works okay there's not much need for that export function. I admit it would be cool though. At any rate, now is not the time to work on it, VCV Rack v1 is close to a release date and the code is still unsettled. If you do want to put any effort into it, you should probably wait until v1 shakes out after its release, let things settle into stability.
Thanks again for all the help, Rory, it's much appreciated.