Most likely, none of this.
I feel like Luigi is pretty fair. Not sure he needs a nerf.
Priority is based on % damage. More priority would entail a damage buff.
I know, it was just a wishlist, since I guess they don't even care about customs. The Pac-Man grab/dair buufs need to happen, though, since those two points feel particularily bad about him, especially the grab, which is bad enough that using it doesn't feel like an option at all, and makes mix-ups harder when his viable options are all about hitting shields with attacks.
Even with increased PKT damage, I don't think it'd be all that broken. It's slow as a snail and doesn't offer enough incentives for you to drop the regular PKT, which is an amazing harassing tool.