should sh and scp be subsystems also?

[Tim Nelson]

I've run into several instances where I want to give users access only to scp or sftp. Now I know that there are custom shells out there with this ability. However, wouldn't it further simplify the core sshd code if sh and scp were implemented as subsystems, thereby lowering the chance of flaws in the core code?
I wouldn't mind putting some work into doing this patch myself if it is approved by Markus or Theo.

Regards,
Tim