This feels like a long time coming. Both methods are a risk, and I wish them luck. Personally, I’d go into Maintenance mode, and start the project anew. It’s seems more daunting, but I believe it’s the better option, in the long run.
What are the advantages of going this route?
Newpipe has hundreds of contributors, and years of work. Some people have left, while some people have forked, because they want xyz feature. When you want a fresh start, in my opinion, it’s best to look forward, not back. Stypox already said that they’ve tried implementing the new (the player) into the old, but it just lead to more problems. To quote:
Although now the code is a bit better, new crashes and unwanted behaviors have arisen, because the interaction between the old and the new code is not optimal. We tried again and again to debug the problems, without luck.
Now expand this across the entire project. Issue tracking and solving can already feel like wack-a-mole, but now you need to figure out if this is an issue relating to the old, new, or even if it’ll even be relevant, once Theseus has been completed. This can lead to overthinking a problem, to high stress, and potentially burn out. Start anew, on new standards, new architecture. Maybe the people who forked the project will come back, and contribute to the rewrite.
That being said. No matter the route, I think this should be decided by the people who’re doing the actual work, and less the community. It’s all good to say Route A or B, but if your team/group is leaning more towards one way, follow the team. If they prefer another route, LISTEN. People’s time is the most valuable resource, and both routes will require plenty of it.