I think the biggest issue with the standalone camera market is that the technology seems to have stagnated; there really aren't huge upgrades in newer models.

Mirrorless models are at least making some progress with creative use of wifi features, better camera designs (Fuji X100 series for example), 5-axis stabilization and quality lens choices. But in the DSLR market, I really don't see significant improvements being made.

I do think lenses like Sigma's 35mm and 50mm ART, with its price and performance, would attract *some* people back into the FF DSLR market, but I don't think it'll be enough.

Indeed, but mirrorless sales has been stagnant while DSLR sales has plunged. Furthermore, majority of ILC (interchangeable lens cameras) are people above 40 (67%), men (80%). And this crowd will get older soon with much lesser spending power.

TL;DR - most mirrorless sales came from people migrating out of DSLR. However the camera trend seems to be dying with the users of the generation (above 40)