I was looking into doing something for my own use, and you can't even retrieve your own list of followers or blocked users in one go! You have to paginate it, each page is counted against the rate limit!
That's what killed off Falcon Pro. The author released a version of the APP with a secret way of putting in your own API keys and I used that for a bit. Then he released a new version, but couldn't just grant the old people access because it would quickly reach the rate limit.
It was about that time I just totally abandoned Twitter.
Use Mastodon/Pleroma/Misskey. Fuck lock-ins. ActivyPub forever!
I don't understand what is the issue if user can add their own keys - just release the app with default set of keys or even without and let the user set their own.
Other than that, indeed Mastodon and co. are great. :)
No joke. I maintain a bot that interfaces with the Twitter API to take in tweets and post tweets from specific users in chat channels.
I read this blog post to determine a) what I need to do to port to the new API and b) how much this privilege of using Twitter will cost me, and it is mum on both of those aspects.