Hi
@RockstarStanley, welcome!
This question has come up before in various forms, and the answer always comes down to how many people would be willing and able to contribute.
I still believe it's doable, but it's always going to be a huge undertaking that will need so much manpower to produce something even remotely similar to the original PotC.
Going open source may well be a good way to do this, but it does mean
everything needs to be made from scratch (unlike NHR where the goal was to port over content from PotC and gradually replace it over time with custom assets). Everyone involved needs to be OK with their work (code, models, textures, audio, etc.) being freely available as part of the project on a public repository, and for artists in particular, this could be a deal-breaker.
The good news is that, at least for Unity, there are more good free assets and demos now that would serve as a good starting point. The Boat Attack demo has a good-looking water shader, buoyancy system and drivable boats (albeit motorized instead of sail-driven), so I'd recommend checking it out:
Verasl/BoatAttack
My advice to anyone thinking of doing this would be to start tinkering in Unity or Unreal and see what you can do. Start a public GitHub repo so anyone can get involved and see how it goes. Even if it starts out as a disjointed mash-up of different tech demos and features, it will help you to figure out what's possible. Just know that it will take some serious time and dedication to get even the basic features implemented, such as sailing, ship battles, land exploration, combat, dialogue and so on.
I personally can't dedicate time to projects like this any more because of my job as an indie developer, but I will say that it's taken myself and two other devs just over two years* to develop
Buccaneers! to a stage where it's starting to resemble a playable beta, and there's still a
lot of work to do to polish it up. Pirate games are hard to make.
*(It might have taken less time if we weren't developing for VR and non-VR simultaneously, but it's still a lot of work!)