Is Stadia multiplayer option available on all games that have it? Is cross platform play open? Or can we only play with other users of Stadia? I'm looking at getting BL3 when it drops. Have friends on PC and wasn't sure if it would cross over? If you can't do you think they will have an option for it later on?
All current games are limited to Stadia. I can't speak on upcpming games like Borderlands though.
It's up to the devs. I imagine it's why we haven't heard anything about ESO is because they want to make it PC crossplay. I know farming sim will be cross play but as far I'm aware it's the only 100% confirmed cross play right now.