Disk brakes are less of an advantage when crawling trails than they are when racing. I'm not crying my eyes out at night because none of my XJs or MJs have rear disk brakes.
Offsetting the possible advantage of the 8.8 having disk brakes is the fact that it's narrower than the XJ/MJ axles, so to run even stock tires on stock rims you need spacers. The XJ 8.25 is already the correct width, so just flip the perches to where you want them and you're done.
Rear discs do not pack up with mud like drums do