Unfortunately I don't think the Patreon model would work.I think that if YsNet had to go a crowdfunded route (which I don't think will happen), they'd be better off going with a recurrent support model similar to Patreon rather than trying Kickstarter again. The blast of hype that propelled the Shenmue 3 KS just wouldn't be there and it would probably max out in the $2 - 3 million range.
Pitching instead for a few dollars a month from the dedicated fanbase I think would bring in more money over the course of development and allow them to offer a set of simple rewards that don't encounter the scope creep and confusion we saw with the Kickstarter reward tiers.
If they were to do a Kickstarter now would be the time. The Yen is incredibly weak against the Dollar and the conversion would be very favorable for a Japanese developer.
Yu said it was difficult to work on Shenmue III without a fixed budget, and funding production on a variable monthly basis would exacerbate these difficulties tenfold. It makes it difficult to hire more people or even keep the staff that you've got if your ability to pay wages can rise and fall each month.
If fans are going to play a hand in funding Shenmue IV, it'll have to be the extremely wealthy ones or those in the business with access to capital (like Sergei).