In theory yes... but no such remote exists right now.. not a rc6x or an rc7x.
I'm not sure how the rf standard works but my original statement was meant to imply that I did not personally believe it would make sense to support the previous rf proticol moving forward. Newer boxes are going to migrate to the rce or whatever format for rf. Yes directv can design a new remote in the style of the rc6x with this but I doubt they would.
