Speaking as someone who feels very alone and plays mmorpgs: its an extremely poor replacement. Nothing more than an unhealthy coping mechanism, like drugs or alcohol.

Sure its possible to have a healthy relationship with such a thing if you have fulfillment in other areas of your life, but if you don't its not good for you.

I think perhaps it would be possible to design something that pushed people together a lot more, but if you were going to do that it would probably be better to work on actual real life social engineering, making meetup groups etc.