I would welcome followers with open arms... because seriously, I don't always want to deal with other people.
Guild Wars is a perfect example of a mmo where having NPC's as party members works really well. Granted GW does many things in it's own way, but it really works. Not to mention that GW is probably one of the most succesful mmo's on the market.
I am by nature a solo kind of a player. I prefer to play my games alone, because that is how I get the most immersion out of a game. I often become so immersed in the games I play that everything around me sort of... I guess you could say, no longer exist. I don't remember how many times I have heard people shouting at me, "HEY! MICKE! Are you listening!?", because I was so immersed into the game that I did not hear them talking to me.
I am actually the same way when it comes to reading books, watching movies/series/etc, almost anything I do. Unfortunatly this means that if I have to focus on something else at the same time (like talking to a person, be it real life or ingame, as I am playing the game), my immersion in the game compleatly goes away, and sometimes it takes me a few minuts to get back into the... "the zone", if you will. It's like trying to read a book when someone keeps randomly turning off the lights. If I took a guess, I would say that my productiveness in a game goes down by atleast 75+% if I have a conversation with a person at the same time as I am playing the game.
During the 5-6 years I have played mmo's, I have NEVER played any of them for the "community", never played them so I can talk to other people, never played them to be social with people. I play mmo's for the same reason I play any other console/PC game. I play these games for the game it's self, to experience what the game has to offer, to see where the story goes, to build up my character, etc. I would never play an mmo, which I did not really care that much for, just because my best friends might play it and want me to play it as well.
So, being able to have NPC party members in an mmo is in my opinion a really good idea. Because it means that you don't always have to deal with other people all the time, it means you don't always have to have other people with you, and it means you don't have to wait half an hour to find all the people you need to do a quest/mission where you need a full party.
I don't think that the npc's has to be as good as your character either. They could be 1-2 levels lower then your character, or generaly have lower stats then an actual player character. Which would make it a bit more difficult to do some missions, and make it almost impossible in otheres. They could even add that for each NPC you have in your party you earn x% less money and/or stuff/resorces, or a bonus x% money/stuff/resorces for each real player in your party, which ever. Or why not both of them at the same time. I would not mind all of those things at all, because I just want the ability/option to not having to deal with other people every single moment of the time in an mmo.
Edit: Actually, here is something interesting about when it comes to my years with Fallout (roughly 10 years or so), and the topic of followers. I have spent more time playing Fallout Tactics then all other Fallout games combined. For each time I have started a new game in FO1 or FO2 (or even FO3), I have started 5-6 new games in FOT. FOT is actually one out of less then a handful amount of games which I actually replay (from start to finish) atleast one time every 1-2 years. Games which I replay roughly 1 time every 5 years can probably be counted on no more then 2 hands.