From reading about P plus, and also the known issues. I would vote to include it in the main game, as this seems to be the only way I am going to be able to experience it.
I am playing on PC, and have mods installed for other maps, and can't get P plus to load at all. Or rather, it does load, but gets all the way to the end of the loading, then exits before I can play.
I think perhaps, if it is part of the main game, it will be more compatible with other things, and therefore actually playable. I have been recommended P plus by a few people, as it enhances the parts of Ark that are my fav bits, and so am sad that I can't get it to run.