There are always 'rumblings'.
I suspect any Ultra Pro Plus or whatever would just add what people have complained is 'missing' from the Ultra.
So a coax digital in, balanced outs, stereo sub outs. Maybe 'better' things which are not yet as good as the rest, so a better headphone out and a better ADC input stage. And finally a bigger screen and/or some sort of provision for creating a display on a third party screen, be that HDMI out or wireless/screen sharing.
I'd upgrade to that. There'll be some things on that list people don't want, but we're looking at the toppermost, end-game product here, so just throw the kitchen sink at it. The only thing I think they might do without is a better headphone amp. Of all those features it's the one which would add the most extra money*, and people can buy their own if they want one - you can't really buy stereo sub outs to add.
* For the record, if it's an 'end game' standard headphone amp, with bags of power, transparently low levels of noise and distortion, and balanced out, you're looking at adding a minimum of £200/$200 just for this one feature, and I'd think they'd only want to add that much in total for everything.
.
