I don't doubt yu' story telling ability the first 3 games to me anyway were beyond amazing in every aspect and possible way, but maybe he needs a more modern up to date with the times writer to spice things up abit for part 4. Like a shared partnership. Someone who can be or play the role of a guide of sorts of what people would like more of, what should be more included storywise and more importantly someone who can say there's a limit here. Yu always wants to do more and give more in his projects but sometimes he needs to be reminded and hear that this is enough let's not push our luck.
Hm...
While I do think it needs to be emphasised that players expect more out of the story and characters next time, I don't think Yu Suzuki actually sits down and writes his games in the same way someone like Hideo Kojima does. Yu is the source of the story and characters, but the games are ultimately written by others and subject to the same resource constraints as anything else.
Someone in a "Head of Narrative" position seconded to Yu might work out, though. Game Director is a very busy role with a lot of people reporting up to them, so having someone who can handle day-to-day story and character work with a fine-grain eye on the detail would be beneficial. Ultimately though, a truly good game is able to marry story and gameplay seamlessly as one drives the other in new and interesting ways.
A few examples:
Narrative: Ryo's defeat at the hands of Lan Di has given him a crisis of confidence, and to strengthen his resolve he must train harder than ever.
Gameplay: New training mini-games, enhanced and expanded RPG and stat system, overhauled combat.
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Narrative: Ryo, Shenhua, and Ren are now a travelling trio with very different personalities and backgrounds.
Gameplay: An expanded dialogue and affinity system focussing on the Ryo/Shenhua/Ren interactions, building affinity with both, losing it if you side with one over the other, and opening up new mini-gameplay branches based on those decisions, etc.
(This is also a great way to display characterisation. Example: Ryo is asked about something he doesn't really want to talk about, the player is given the option to open up if they want, but also the option to clam up. If Shenhua is asking the question, he'd take a softer tone "I don't want to talk about it", but if it were Ren he might take a blunter "It's none of your business" approach. In a gameplay system they might both be affinity-losing answers, but it says a lot about Ryo's character when he shows different sides to himself depending on the opposing character in the interaction)
As for an "up to date writer", I... dunno. Depends what you really mean by that. This is of course subjective, but a lot of writing today is terrible and phoney. People who read every book on storytelling going but didn't understand them at all, so construct a bland paint-by-numbers pantomime, and don't really respect the tone or period they are trying to portray. I believe Shenmue III dub director Bill Black said a few modern words almost slipped into the English language translation of the game until he intervened to remove them and replace with something more... 80s. Sometimes modern isn't automatically better. Doesn't mean getting an old school writer either, just finding someone who takes a real passion in the work besides the superficial.
Shenmue II adhered to the classic form of a simple story told well, or simple story/complex characters. That's the benchmark, I think. Maybe with 15-20% more action sprinkled on top.