[FranOntanaya]

Part of the solution could be to separate connecting from subscribing. People feel they would lose some kind of social capital from unfollowing an existing connection, but would rather not see most posts from that account.

I don't put much value on Twitter's social capital so I arbitrarily stick to 150 accounts. That seems to work for me.

[SyneRyder]

You can do that already, in a way. Twitter lists provide a way to 'subscribe' to someone's tweets without actually following them and putting them in your main feed / letting them DM you. I love @SwiftOnSecurity, but she tweets too often for me to follow her, so I have her on a separate InfoSec list, together with @TroyHunt and others.

If there's someone you feel socially obligated to follow but find annoying (or they decide to go on a rant one day), you can Mute them and you'll still be following them without seeing their Tweets.

I find Twitter only works if you can be ruthless in who you unfollow. As soon as you worry that unfollowing someone will offend them, it starts to fall apart.