I've used ProTools since version 4 and have been on Studio One for a couple years. I always bounced mixes in PT in dual mono format and mastered them in dual mono until the final export of the project when they became interleaved. Without starting a controversy about this, I could hear the difference as do many professional mixing engineers.
I would like S1-V3 to provide an option to export mixdown as dual mono. It would also be critical that the Project Page be able to import dual mono tracks. I know that even for users of PT to record, the Project Page is a great drawing card for S1-V3. If it could handle the dual mono mixes that would certainly open the door for a wider audience of users.