It's highly likely Masamune will be added some time in the future (it was the SAM level 99 Empyrean Weapon in FFXI after all), given it's a reoccurring weapon throughout the FF series.... but don't expect it to be FFVII's version. Most likely it will have an original (and presumably fancy) design that will look nothing like previous incarnations.
But yes if SE doesn't end up eventually adding it to the game, I'll eat my Curtana.