The problem is that none of us has done such a big rewrite in their short time as developer.
We therefore need for feedback and help! We have listed our ideas and plans in detail on GitHub: https://github.com/TeamNewPipe/NewPipe/discussions/10118
Some open source projects have failed their rewrites, got stuck and vanished after no development happened for too long. If you have experience with rewriting a whole project, please give us feedback on our plans!