Is that a serious question? Social networks are dependent on network effects. Having a subscription immediately increases the barrier to entry too high for people to be able to get their friends on the same platform.
My feeling is that we have entered an age that youth is not naive anymore and would happily pay $3/month (at least in the US) for a non-tracking all-round communication service.
As long as no one else they know sees...
Probably not, but there just might be enough, youth (or people just out of the edge of that category with contacts inside of it) that will pay $10/month for such a service plus the privilege of sponsoring 9 of their friends with free accounts. Who, would of course have the option of upgrading to paid, getting their own 9 giveaway accounts, and returning the giveaway account to their sponsor.
Which, sure, might be as little as $1/user/mo., rather than $3.
Are you joking? When I was a broke student there was zero chance I would sign-up for a monthly subscription service.
It's a pipe dream.
It's not that "oh, if it'd succeed someone would have done it by now," but the attempts I've seen at this make me think that it'd be very difficult to even try.
We have yet to learne to pay for nice things on the internet.
Network effects are king.