The tenets of the immersive sim have also spread their roots into the overall medium as a whole as well; look at BoTW or the promises of the upcoming Assassin's Creed, among other games big and smallI don't see the need for doom and gloom. In the span of just over a year, we've had Deus Ex, Prey, Dishonored 2, and an upcoming standalone Dishonored 2 expansion. As a lover of vent-crawlers, this is an embarrassment of riches. What other time has been so active for the genre? I think these games have proven a market exists for immersive sims, even if the market is out of step with expected financial returns from traditional AAA publishers. The genre may go on to live at the scale of System Shock 3 or crowdfunded games like Consortium. I think that's okay.
There are developers out there with talent and passion for making dense immersive sims. There are fans out there willing to pay for immersive sims. Something will happen, just maybe not on the scale of a title five years in development at one of the largest publishers in the world.
Another game to keep an eye on is Copper Dreams. It's a cyberpunk CRPG, but it has a lot of immersive sim DNA