How would this effect SSPX  ?

From what is known, it would be a return to the indult — with a prior authorization of the bishop [as under the motu proprio Ecclesia Dei], or of the Vatican — with all that it entails, that is, a reintroduction of the prohibition of the celebration according to the Missal of St John XXIII, so many denials of authorizations, and the ghettoization, in practice, of the priests and faithful attached to the old rite. After Moses, the Liberator, Pharaoh returns. [Source]