The only argument against a CSS rim is that some find the braking to be not as good as with a standard aluminium rim, that hasn't been my experience, I don't know why there's the variation, though I respect that some others have found it so. Well, there's also the price, but the longevity, accidents permitting, should make it better long term value.
So bearing that in mind, and also that around 80% of your braking is provided by the front brake, and that not rebuilding Rohloff wheels is good for their durability, and the lack of wheel builders with Rohloff experience... It would seem to make sense to have a rear wheel that needed infrequent rebuilding, which means disc or CSS, regardless of the braking you choose for the front.
Rebuilding a wheel with a rim of the same ERD isn't complicated, though you may not wish to do it yourself on such an expensive hub. Professional wheel builders have their own ideas, and there's a surprising amount of variation. What you want to avoid (I learnt this from experience) is to be rebuilding the wheel any different to the way it was originally built, that includes the same spoke pattern, same rim size and same tensions. Sometimes the only way to be sure of those things is to either return it to the original wheel builder, or do it yourself.