From looking at the bug tracker, it looks like Garry intends to eventually add collision hooks. Anyway, I made a module to add collision hooks on the server (calls into Lua). The only side-effect is that you need to set it SOLID_NONE on the client to produce proper prediction when walking through an entity.
You can use this to make a proper version of UClip or something, or do TF2 style doors.
How to use:
- copy Release/gm_guardian to lua/includes/modules
- modify ShouldEntitiesCollide to fit your needs