Primacy of tenure is an odd one - it's to do with the sport more than actually who owns the stadium.
Sale Sharks did have primacy of tenure at Edgeley, and are equal shares of Salford - however because at Salford we're sharing with a Super League side it doesn't matter.
The reason they want you to have primacy of tenure so if Sky want you to rearrange a game you can do so with no fuss - Sky have the right to Super League as well so they're not going to rearrange a Sale and Salford game for the same day.
Still doesn't make sense for teams like Irish, Wasps, Sarries who all share with Football sides, it's just straight up hypocrisy from the RFU (shock horror!).