My take on the cleaning up the App Store(s)

Point 4: Insist on Retina... I think there's a better way to do this than you suggest (time-limit before they're kicked for no retina support).

Start enforcing this rule after, say, 3 months - to give devs enough time to comply. From then on, any app which is either submitted (for the first time), or updated, needs to have Retina support, or it gets rejected.

This stops apps unexpectedly disappearing, e.g. if someone has other commitments than iOS development, whilst ensuring that all well-updated, still-supported apps start to support Retina.

I wouldn't be surprised if Apple did enforce something like this if (when) the iPad 3 gets Retina support.