This would even be compatible with him wanting Luke to strike him down in RotJ- his spirit could pass to a child of either bloodline, making the ending of RotJ an apparent Win-Win for him, failing only because he wasn’t truly struck down, but chucked away by Vader out of love for Luke, not anger at Palpatine.

It also makes sense that he didn’t inhabit Vader, since he was unexpectedly crippled at Mustafar. Any of these four (Vader, Luke, Kylo, Rey) could have been apprentices until they became hosts- also having Palpatine cheat the rule of two (the apprentice must supplant the master) by making a bloodline that he’d take over in continued life even if they followed that doctrine.