The 80D is only 3 years old. I know that lately the xxD series has refreshed every 3 years or so, but nobody who owns an 80D should really be desperate to upgrade to a 90D. The 7dIII may be arguable, if they did want the higher FPS/better AF spread. But I can't imagine what a 90D could have that would be revolutionary over the 80D
Oh, there's plenty to improve, and three years is a long time. The 80d was never class leading, even when it came out. New sensor for better dynamic range, improved high iso, 4k, 1080p at 120fps, more and better distributed autofocus points with improved DPAF and face/object tracking, etc.
But as @QuisUtDeus said, in a few months the RP will be on sale for what a 90d would be priced at. It's too bad, really. If they had spec'ed the RP just a little better they could have pushed most of the 80d/7dii owners into full frame, the rest could be funneled into EF-M, and killed off the EF-S line. Maybe they still will, depending on how RP sales go.