The big Johns Wally West Flash TPBs were originally hardcovers as well.
The first Batman Inc and the new Batman and Son collections were also deluxe hc's before getting tpb releases.
The new Flash collections seemed to me just part of DC's recent trend of big trade paperback collections of older material that just happened to match the page count of the first Flash omnibus, rather than actually being a paperback version of the Flash omnibus vol. 1. And Batman Inc and Batman and Son, yes, but those are fairly small and were not collected in trade form, so it made sense. With GA Lemire, they're already collected in trades, so it seems very unlikely that they would do a paperback version of the deluxe edition anytime soon.
I was originally meaning bigger collected versions more like Swamp Thing by Scott Snyder Deluxe, New Frontier Deluxe, Solo Deluxe, Batman Year 100 And Other Tales Deluxe, Crisis on Infinite Earths Deluxe, etc.
But, yeah, you're right. It's not as infeasible as I had originally said.