I know there is co-op, but could online multiplayer be possible? Just a thought
Online multiplayer is on my radar, but not planning to come out any time soon since I'm still learning how to do it properly. I might get started on an early prototype since a lot of people want to play with their friends (including me). Though it might be a peer-to-peer type of online with manual port forwarding first then I'll move it up to dedicated.
If you do want to play with friends online, I do recommend Parsec. It streams your screen to your friends and they can connect to your pc and play 'online' with you.