I think he meant that no custom dynamic scripted models such as weapons,npc's etc will be usable for now as it always was. Static scenery models have no restrictions in MP so you can build your level designs with no issues.
Doesn't mean you are entirely limited to stock, but just in case you might want to confirm that one. If you can only build your levels for MP with stock models I would say it was a pretty pointless feature and would have limited appeal.
If it were the case I would simply swap out the meshes and textures and challenge GMAX to notice it....whatever it doesn't make sense that all custom models would be defunct.
As said above it was always underused so not many around here to confirm things, personally I only ever created one MP game and that was Reloaded back then. All of it was custom and weapons were stock which was no big deal, pretty sure you could use custom characters just fine as players but would likely be stock animations only.
