It exists already and is supported in a bunch of clients
Discussion
Unfortunately there are virtually NO clients that support robust list management in the way Twitter did.
I have an open bounty for Amethyst. Id set one for Damus as well if there was interest, along with a browser client.
An ideal client would allow for the creation and management of follow sets with ease of adding and removing entries
this is surprising to me, I was told that many apps have this already. It's next up on our roadmap after push notifications!