If there is one thing that needs to be re-written and consolidated it is the arrs ecosystem. Replacing/consolidating the arrs themselves is pretty straightforward. The trap that quickly becomes a token incinerator is incorporating the downloader into the library manager itself. A lot of learned lessons in that sabnzbd codebase.
As someone with coding projects in the is area would you care to elaborate on "a lot of learned lessons"?
sabnzbd is basically packaged decades of domain specific knowledge about deobfuscating media files