the double-layered vest/waistcoat: when did this become a thing?

Meaning This, with the word “formal” attached. I mean, I was glad vest came back after being banished during the 90’s for having been abused as 1970’s disco & 1980 Wall Street costumery. But still, two of them at once? And with the bottom button not undone? I cannot tut the appropriate level of tuts.

This look, while not my demographic, is different - the vest equivalent of multiple polo shirts with popped collars, no presumption to formal dress. (my only objections are that the outer vest may be improved with lapels; and braces, never belts, are worn with waistcoats. When you wear a belt with a vest it looks like you’re missing your holster and cap gun)

Does this mean that when pleated trouser return as well, they’ll try to revive reverse pleats?

I think that this will not last longer than the spring, and will go the way of the Edsel.
Only about 60 more people in the Republic will buy it, and wear it once.

Only if you wear it with plaid pants, a checked jacket and wingtip shoes, and none of the colors must match.

Two waistcoats were a fad around Samuel Johnson’s time, IIRC. It’s not new.

Nor good.