Rugby Championship starts two weeks after this, so that rules out UK based Pumas/Boks/Wallabies (2 weeks quarantine going into Aus, so they'd miss the first game and all the training, if they set off after this)
Apparently they said on the BBC Podcast that any player who played in the prem this season and will again next is ineligible (due to the short turn around).
So they can choose from retirees, players moving abroad (though I think the Japan based players will all be off soon, as there's a two week quarantine going into the country and preseason has just started), and Super Rugby players who aren't playing in the Rugby Championship and don't mind the 4 weeks in a hotel room.
and maybe like RFU Championship and Pro D2? I dunno if either have even started pre-season yet/have kickoff dates
Everyone make sure your phone isn't on silent cause I think some of us will be getting the call at this rate!