So... has he given a definitive "yes" or "no" response, or is he dodging-and-weaving with the best of them?
Yes is the answer. Yes has been the answer ever since the games announcement in 2014. I watched every single interview and Sean has ALWAYS mentioned that you can play with other people, you'll get to find out what your avatar looks like once you see ANOTHER PLAYER, you can grief and DM others if you see them, you wont see a nametag over them so you might miss players that fly past you.
I don't get how people are in denial about this and say "he never promised MP", yes he did and you can look it up (the talk show interview is one of the more recent ones where he outright says you can run into other people).
BUT then there's the game launch on PS4 with people reporting that no position data is sent to the servers (which doesn't really mean anything though, they'd probably use P2P anyways and potentially try to connect you to players that are in your solar system? That's how I'd do it: whenever you request data for a planet you also get flagged as in that system so you're ready to get paired with whoever enters said system too).
They probably realized they couldn't finish the MP aspect in time for launch and scrapped it.