if I can get some spare time during holidays, I would put a snapshot of stable with 3d-viewers add-ons on sourceforge…
are you on windows or ubuntu?
I just put a 3d object associated to e.g. a hole/pad and I assign it as virtual
(check the Virtual Attribute for the mechanical part in Footprint, Edit Parameters, Properties)
then I toggle ‘virtual’ models visibility using my menu button…
I toggle only 3d modules (wrl files) and not pcb footprint, so in case of a spacer anchored to a pad, the pad will always be displayed, but the spacer only when the virtual 3d modules will be enabled…
in this way you can assign mechanical parts (e.g. enclosure, add-on boards etc) to virtual and decide when you want to display them, during board design
I think the easier would be to have your own lib in github, so they will be available for merging…
I’m going to package some models to fit in the standard kicad libs, so I will merge the models there
Please I just would need to have some rules respected, as in the first post…
I think a try would be fine, but I don’t think they are still ready to accept FreeCAD models… which is a quite not smart choice, considering they are going to develop the 3d-refactoring to accept MCAD models…
I already asked few times…
anyway a try would be worthwhile 
Maurice