I'd like to add more thoughts:
Another game of this generation that was a(decidedly) niche title and ended up doing well was Kingdom Come: Deliverance. It also has a sequel that has been greenlit, despite it not setting the world on fire.
Nostalgia is at an all-time high. One might argue that Shenmue is still an appeal to the way games used to be. When done correctly, it has massive reverberations with everyone who holds something dear. Some examples of this are Cobra Kai and Ghostbusters: Afterlife in the movie world. In the gaming world, Eiyuden Chronicle and Bloodstained.
One game that was subsequently trashed years ago was Duke Nukem Forever. It was lambasted because it "played like a 20 year old basic shooter". Technical issues aside, that was the whole point of it.
It's a way for folks to see just how many things, such as QTEs, day and night cycles, NPCs with routines, became mainstream from one series and are taken for granted as commonplace now.
YsNet now has experience under their belt from making Shenmue III. They aren't under a constant deluge of pressure to "show something" or "get it out" and have a lot more knowledge of the engine being used. So I expect Shenmue IV to have a lot more going for it when it comes to detail when it is shown.
In addition, they know what fans liked, what they didn't like. I would expect IV to address things like the battle system, the Stamina system, etc.