Hi Girish, Welcome.
Have a search of the history of the mailing list here. There was one, or a couple of (?) threads on adding a Redis backend recently (last year or two).
From the "Why Redis" section of your proposal, I think the answer is simply that lots of users (most in fact according the recent survey) are using Redis for caching, and we a should have a backend in core for that.
The scope is JUST to satisfy the cache backend API, and no more. It's a non-goal to deal with any other Redis features, so various data structures and such is not relevant. (Third-party packages would could offer things in this space.)
For the work breakdown compare the recent PR adding the pymemcache backend. #29887
— the project would be similar in scope.
The ground here is well-trodden, so most of it is documentation — we need to be very clear on requirements, installation and setup.
I hope that helps.