not totally up on the versions of XML MIDI, however I do know more than a few Sibelius users who work in 7 and 7.5... One might hope that reaper could accomodate that version of XML import\export even if they currently target only the 3.0 for Sibelius 8 I have no idea how much coding it takes to deal with the XML in and out but do hope for the future reaper versions there could be that kind of backward compatibility???