I disagree that the 5.1 mix on the DVD-A can't be bettered. Sonically, it's an absolute revelation compared to the original mix, and it's worth having for that alone. But in terms of instrument placement it's incredibly conservative and not much more than 'big stereo', sort of like the Tom Petty 'Hypnotic Eye' 5.1 mix. There are elements that are unique to the front speakers (drums, bass guitar, vocals etc.) but there's nothing in the rear speakers that's entirely discrete, all the horns, pianos, guitars etc. that are in the rear speakers are also in the corresponding fronts as well which basically makes them sound like they're coming from the side walls rather than surrounding you or behind you at all.
There's no reason to think Steven can't better this, not to mention that whatever he does will surely be more dynamic than what's on the old DVD-A which has about 3dB of dynamic range compressed out of it and leaves it feeling a little bit crunch and inorganic for my tastes.
I also hope that whatever's coming out includes the original quad mix, which to me is fantastic both because of the extremely aggressive instrument placement, but also for all the extra bits of instrumentation that ended up in the mix (ie stuff like the extra lead guitars and acoustic rhythm guitars in 25 or 6 to 4 for example) that make the quad mix even more of a bonafied 'alternate mix' even if it isn't entirely true to the original stereo mix.