Good idea Floris. And yup it could... but it might get messy as that's effectively saying that each rewrite rule should be applied based on usergroup... because don't you want your premium members to have YouTube rewrites too? I'll look at everything on|off per usergroup, and consider more granular stuff later.
All of this is on the backburner for a fortnight though. My nan died earlier today, and so until after the funeral finding time post-work to concentrate is a little difficult. It will be done though as it remains incomplete for my own needs.