seems like we getting into semantics a little bit, what MMO is and what not: Wiki Definition is as follows
I highlighted a couple parts there as it does not state it HAS to be. the second part, we have to see how the promised Wings is going to be.
Now, nowhere does it seem to say that all players have to be able to be all together in one space. it does allow a large number of players to be on simultaneously, in the same universe after all, solo, groups and open all share the same universe and everyone affects it, albeit in a minuscule way. If you look at some threads on here, people claim to have started expansions into neighboring systems by supporting factions. so looking at it this way, i think the label still fits.
as it has been mentioned above too, WoT is defined as an MMO, other then over the sight of your cannon you don't see or meet other people and even then, its a matchmaker that puts you in a room with 29 other people, or less.
i think a big unknown right now is how Wings will change this game, what it will bring to the table. after all, this game has not even been out a month. i for one, personally, have fun with it. i do play open and i run into other players fairly often now that i returned to the core systems a bit more from the frontier i was in. most people don't even talk when you give them a friendly hail. guess they out there looking for giant space rats
Edit: you guys want going to make me want to fire up WoT again, lol