I hope that if we get a Shenmue IV, that its gameplay will combine the intricate detail of the first game, while offering further expansion like the second game. One of my only criticisms of Shenmue II, was that it felt more streamlined in comparison to its predecessor. That being said, one could argue that streamlining Shenmue II allows for a more free flowing combat system. So I really hope for the best of both worlds in the next entry.
Yeah, that's the dream. The problem is that size and scope have a direct impact on level of intricacy and detail. You don't even have to look as far as S2 to see this in effect. In the original game you start in the most interactive and detailed environment in the whole game. Once you leave the Hazuki Residence, the level of interaction drops a bit. It's still very high compared to lots of games, but due to the larger outdoor environments you can no longer lock on to almost any object, lift the lid on boxes, trash cans etc. When you're in a shop you can look at various items, but you can't open fridge doors, examine everything individually, etc.
Then with S2, the scale increased so much to the point that it was impossible to give most NPCs personalities like they had in S1. Examining things went almost out the window entirely, apart from a few specific scenes. In all honesty, though, I don't think they sacrificed too much in order to pull S2 off. They struck a good balance between scope and detail, with some areas still being pretty mind-blowing in terms of visual detail.
I know it's been pointed out a million times but S3 is somewhere in between. Bailu feels most similar to S1, with just enough daily routine and characterisation in the NPCs for it to feel convincing, and homely. Lots of examining things...some would say they went too far in this direction on occasion. And Niaowu feels most similar to S2, with the NPCs that walk around being fairly useless filler (not really a bad thing), with shop owners and "special" NPCs being the main source of characterisation and progression. The main differences for me between Niaowu and Wan Chai, for example, are that A) the characters are more fleshed-out in Wan Chai, B) the side activities are way more robust and fun in Niaowu and C) Wan Chai is a bit more convincing due to the density of the crowds.
Personally I would be really happy if they focussed on those slightly smaller, Bailu-esque environments, so they could fit the characterisation in there. There is definite appeal to huge bustling cities, but what I want most in S4 is better combat and better characters. Keep most of the side stuff that's in S3 -- fishing, herbs, love it -- but focus on characters and improving combat. Definitely keep the investigation sequences but tone down the frankly mental amount of drawers you can open