Sounds interesting. I would have to modify or hack a few things to allow for putting portals anywhere (portals do not like to cross with other portals ;) ). I wonder how it would actually work in a PvP mode. It could be fun when doing so but annoying when being shot at. With all those hands appearing on different surfaces and shooting at you. It would have to be carefully designed and well playtested to make sure it is fun. For now I don't plan a PvP mode, but I will write down that idea.
I wanted to have small enemies appear through portals on walls but these would just function as holes, not as something that appears and disappears. Still, could build something around that idea.