I never bothered to go through the RotS extras, so I haven't actually seen that, though people here have referred to it several times. Pretty indicative of Burtt's mindset if he has to make his stuff dominate everything else. The prequels as a whole tend to have the music at somewhat low levels compared to the kind of prominence it enjoyed in the original films. Not to mention it is often hacked apart and tracked over scenes it wasn't intended for.
This demonstrates exactly why posthumous remixing of film soundtracks is usually a bad idea. Oftentimes it is done by people who were not involved in the original production, and have no real understanding of what it was intended to sound like, thinking they are improving the film when it is actually becoming worse. Or it could be someone who was involved, but didn't get their way initially, and takes it upon themselves to 'correct' the 'errors' made the first time around. The fact that remixes are quite often the only soundtracks available is especially galling. If all studios had the courtesy to consistently make the originals available alongside the revisions, it wouldn't be so much of a problem.
That is not to say that all remixes are bad; Toy Story, for example, got a revision that was a definite improvement, and some of the James Bond films sound better simply because the music has greater clarity and stronger frequency response, not to mention stereo presentation (though some of the Bond remixes definitely make things worse in other ways).
If by some miracle they actually did release the original versions of the Star Wars films for Bluray, and even more miraculously use the 70mm audio masters, some amount of remixing would have to be done to fit the current format. The two boom tracks were used for LFE effects, most notably the Star Destroyer flyby, but apparently also to increase headroom by augmenting bass response that would otherwise go to the main channels, a sort of global crossover at 250 hz. Present day standards use an LFE channel cutoff at 120 hz, with the effects usually being rolled off starting around 80 hz. Depending how it was done, it may not be feasible to use the boom tracks directly--the folks involved in the 1993 mixes felt that better results were obtained by adding in bass separately from a sound effects master, and this may also apply to any potential 70mm-derived 5.1 version. So the LFE levels would be up to the mixers' discretion; some amount of increase might not be unwelcome. There is also the possibility of introducing stereo panning into the rear channels, but generally the fewer changes made, the better it would be.
This is all hypothetical, of course, as the probability of any of it actually happening as we would want is vanishingly small. I can only imagine what fresh horrors the new mix will bring, along with who knows what sort of rubbishy cgi garbage . . .