Musing:
One reason I believe that Shenmue IV(and possibly V) will become a reality for us has to do with the anime. I think they go hand-in-hand.
Traditionally, I think there is usually a wait between seasons on certain anime. If so, having Shenmue IV become a reality in game format serves two purposes.
It gives Yu Suzuki the chance to continue the series in game, plus it serves to give extra material for a second season of the anime, as the first round has focused on I & II.
So having it focus on Shenmue III and IV helps a lot, both having a different format for folks to enjoy the story, as well as allowing Yu Suzuki to incorporate more depth, particularly to Shenmue III, of which the story felt a bit rushed(probably due to Deep Silvers pressure and overall Kickstarter stress).
Shenmue V would be great to have on its own in-game, but it'd also make for a great "series finale" that you see in some forms.
I see the entire resurrection of Shenmue and rekindled interest a testamenf the sheer power of its fanbase and it could pay off dividends, as it has in other media.
Lucifer was another series(in television) whose fans helped it to be resurrected by Netflix and it ended up having a great conclusion that fans deserved.