The A359R is a normal A359 with less thrust and reduced MTOW of 250ton (so it should have less maintenance costs) but the big thing for me is that the A359R can be converted to a normal A359 with MTOW of 268ton by "paperwork".
Can be converted to a normal A359, with front end payment to RR, and higher monthly maintenance payments thereafter. Presumably an R fleet also provides RR somewhere to hang older engines with performance decay.
I think that there is more to it than just the possibility of converting back to a long haul aircraft.
The A359 is a slightly heavier plane than the B787-10, so there must be something else that pleaded in favor of it other than the reduced MTOW and a low price.
Things that come to mind:
-The XWB has a wider fuselage, enabling faster turn-around times in the same 9-abreast configuration. This is significant for a widebody on domestic/short-haul missions.
-The XWB engines are bigger engines so they can take the cycles at a lower cost. Where the smaller Trent 1000/GEnx will quickly use up the cycles on the hot section parts doing mutliple daily runs, the Trent XWB will be hauling the same 250 ton MTOW with much more ease, saving a lot of money on engine maintenance.