I don't know about all of this. I've seen this bandied about a lot lately, and it's probably the most attention I've ever seen given to shu aging on the internet. I've had shu that's 8 years old, and it tastes absolutely nothing like anything that I've had five years or younger. I've also had shu that was four years old that was "getting there" as far as taste and mouthfeel goes. I honestly see no problem with shu aging longer than 10 years, even. It all depends on it's amount of fermentation. If it's heavy fermentation, it's usually going to be thick and creamy even upon it's release. These shu probably don't change a huge amount over the years. There are, however, a few recipes even by the bigger factories like Menghai that use lightly fermented material to produce their shupu. Usually these lightly fermented shupu carry a chaqi and huigan more similar to young sheng, and so have a clear potential for further aging.
On the opposite side of things, this is all conjecture. I personally have not tried a thin, lightly fermented shu, aged it for 10-15 years, having tried it myself throughout the years, and that's part of the problem. I have some shu that's definitely shown vast improvements since purchase, but this is merely airing out the fermentation flavor. We'll see how my heavier fermented shu stacks up against my lightly fermented shu in the coming years.
As always, drink it whenever you want to. Only times I'd ever advise to drink it is if it starts losing flavor, or anything like that.