InMusic could be just opposed to a partnership like this simply due to allowing integration, an advantage for InMusic mixers’ own recent mixers, to give sales to another company. I guess they could always get some sort of profits split with A&H. I really think opening up Engine to other companies and brands is the way to go, but an MP2023, though, with certain features that put it ahead of the MP2015, while also taking away certain other stuff, would allow the MP2015 to remain in its current position as live-production-style mixer with its master iso also for those old-school rotary house mix DJs, while giving people a reason to potentially want a new version. You might even want both 
I try not to knock the X18xx mixers too much, because they do test nicely in TrueRTA & RMAA, the integration works so well, and they can work even better in the future (more integration, better sound, more effects) with firmware development, but I do prefer rotary. Even just flipping those sweep and fader functions (with adjustable deadzone size for both) to get a DB4-style rotary mode would go a long way. Yet, the low-level detail seems lacking, midrange is a little void of expression & presence, and the summing indeed doesn’t seem great for whatever weird reason on them. That last one, though, mostly seems to be dealt with using more tone controls in-the-mix, and the first issue just necessitates louder volume. On the plus side, the X18xx mixers aren’t particularly strident, synthetic-sounding, or artificially-polite at high volumes, though they are kind of just matter-of-fact, struggle with delicacy, and come off as dry with their poor low-level resolution. They certainly don’t lack physicality to the sound, but as I’ve said before, I would like the option to run them at a lower volume and still differentiate detail and separation as I can do on even the DJM-800, 4D, and d.4.
The weakest link in the Prime flagship separates sound, though, is not the mixer, but the players’ firmware, which needs some substantial audio processing changes. I’d rather listen to a Gemini or Hanpin into an X18xx recreationally than the SC Prime players into the DB4, MP2015, or X1700, to say nothing of an old CDJ into an X1700… but we are talking about DJing, here, and not just powdering wigs and eating grapes while listening to chamber music.