I dont think Shenmue IV happening or not is something we should worry about. As far as I'm concerned, it's happening. People keep thinking about the situation about Shenmue III but these were far different time.
- YS was still working at SEGA
- SEGA was very cautious with their IPs
- Making a game was harder back then because tools were both expensive, hard to use and not widespread.
Shenmue III took that long to happen for those reasons:
- YS was still at SEGA when it was obvious SEGA didn't want anything to do with SHENMUE.
- SEGA was unwilling to do anything with their dormant IPs and was against licensing them.
Shenmue III finally happened because:
- YS left SEGA and was free to work on what he wanted.
- SEGA softened their stance on licensing hence why Wonderboy, Panzer Dragoon, Street of Rage and Shenmue all saw new installements without SEGA's involvement.
- There are tool such as Unity and Unreal Engine which are documented, with support from their providers, easy, fast, inexpensive and powerful to use.
But it took until barely 6 years ago for those things to happen.
Now the question about Shenmue IV is: What are we getting ?