If you are thinking of filesystem binding which is system-wide - imposed on all processes, then I agree this is orthogonal to SUID/SGID.
However if you are talking about per-session filesystem binding (with process-local name spaces that are inherited across fork/exec, but not imposed on other processes), then I think this is exactly related to SUID/SGID.
A problem with SUID/SGID is that so much is inherited from the parent. The process-local name space would be inherited too, so it could affect the behaviour of the program in unexpected way.
This is "simply" avoided by allowing process-local filesystem binding, but only on to objects to which the user already has write access. However I don't know if it would be as useful with that restriction ... maybe it would.