Hello I noticed that Enscape's proxies for Sketchup are also skp files.
I guess this can be convenient for when saving as a proxy something that already exists in your model.
Problem is that skp doesn't seem to be very efficient. For example I use transmutr to turn fbx objects to Enscape proxies, but the skp Enscape proxy is many times bigger than the original fbx. This in turn means that Enscape uses a lot more RAM to load those proxies and probably takes more time to do so.
It would be nice if Enscape could load fbx or obj directly as proxies, or if it had its own file format for proxies that would be more efficient than skp.