Since ARM does not manufacture any chips, I think their interest is only in the 584 patent as it relates to the architecture that they license.  The right justified operands apparently takes the 584 off the table, with respect to ARM.  Not sure if that would necessarily be the case for the licensees, since it my understanding that with ARM architecture you can have either left or right justified operands and it is up to the chip maker to implement one or the other in the design phase.  My understanding could be wrong.  Opty