I'm mildly curious to see if they do end up producing one, but like so many other companies with other products, I think GM has already put themselves in the dangerous position of too little too late, with the ZR2. What I often see with all kinds of products, when this kind of thing happens, is that the usual loyal customers go all different directions. In this case, some will have bought a Z71 and been satisfied, some will just mod a Z71 to make it as good or better than a ZR2, some will go to another brand...in the end, there is a much smaller population of die-hard holdouts from what was a much larger population of potential customers say at the initial release of the 2015 model.
Additionally, what does coming out with a ZR2 say about the Z71 and the Trail Boss...basically it just re-emphasizes that those 'off-road' trucks have mostly just cosmetic versus performance enhancements.
And finally, what are the expectations of a ZR2 after all this time? Better shocks/suspension, better tires, skid plates in a few more places...what can they do performance-wise above and beyond the Z71, that will bring a price premium and differentiate the truck from the Z71. I agree there's definitely room for improvement over the Z71, and I almost didn't buy because of some of those areas needing improvement, but the margins for improvement are not huge and I think it's a tough business decision to invest in these slim margins when all the higher volume trucks are selling so well.
If there's one thing that I see as motivation, it's not necessarily sales of the ZR2 itself, but what it brings to the GM truck brand and reputation. GM builds it's truck branding on toughness. You see that in virtually all specifications and obviously in their advertising, towing capacity, engine horsepower, payload, etc., but in the serious off-road department they aren't the leader without something like the ZR2. Even if the truck doesn't sell incredible numbers, it still builds the brand for the whole truck line, and show's GM's commitment to all that they try to portray in their image and branding.