Considering HTP-1 is still top-of-the-game features-wise except for ART*, I'm not sure what a new model would bring at this point. Maybe Dante? That's only potentially useful* thing that seems to be absent. I guess 20 channels (to run 9.1.6 with 4 subs) is also on some people's wishlist, but I don't see that as likely in this price range. Otherwise it seems the main reason to make a new model is just to change up the faceplate a bit.
*Some will lament the absence of HDMI 2.1 (which seems like a fairly meaningless spec at this point) or some DST-X variant (also largely irrelevant, given that nobody streams content using that format).