You should definitely add a feature where the player could either possess someone who has the halo on (or someone who has maxed out stats/corruption) or swap bodies with them the only things i can think of this being used for though are to increase their stats or maybe for just a different sex scene where you fuck your actual body while controlling one of the girls bodies

Or better yet have a scene with girls who don't normally have scenes together. Example one of the maids with the principal, that would be cool

To your point, we're already extracting their souls (at least, that's heavily implied to be the case,) as part of the Void Queen creation process, so why not take it a step further and do full-on soul transplantation?