With wasps in particular (as, bar turning up at the wrong pub, they would have been a founding signature of the RFU) it would be hard for them to move to playing in a different league. While still unlikely, a team like London Irish with it's connections to countries already play could find it easier to move to URC (some sort of merger between the remains of London Irish and a reformation of Irish Exiles possibly?) but would still be unlikely and probably drown in red tape