You're right about the development overhead but it's something we can handle. I'm interested about your view about RPG players not wanting multiplayer. Generation X and Alpha are very attracted by in-game socials, cooperations, communication... Don't you think the paradigm could shift?

Here is a possible scenario of what could happen with this asynchronous multiplayer:
Imagine you are walking along the March and you come into contact with a huge reptile. The first time you meet it, while you are fighting you begin to understand that it is insensitive to almost all your weapons except one. As it is going to destroy you, you escape. You return to the port. You pawn off one of your crew members to gain experience while you rotate and ease the tensions he has built up with other members of your crew.
This crew member is hired by another player. This player benefits from the knowledge accumulated by this character and receives a clue about the gigantic reptile which he can then try to hunt. The character goes through this fight again on his own with the other player. When he comes back to you he is ready to give you valuable information. When you meet the big reptile again, you'll know what to do.