Should bioware do one final shepard game?

He's says, in fact, "Some of the details have been lost in time.  It all happened so very long ago."

You're trying to make it prove something that is not proven.  I've not done a 180 at all.  Bioware made that scene ambiguous enough that it would fit any ending the player possibly chose.  They deliberately framed it in the setting of an old guy telling a kid a story... a yarn... a tall tale, only loosely based in fact.  I say they can go ahead and continue Andromeda as a sequel and keep all the endings possible.  You're the one who wants to lock it into only the one possible.  In my mind, it's just as likely that Stargazer is Scott Ryder, telling his kid a story (read highly embellished story) about what he found in the ruins of the Milky Way when he returned more than 600 years after the end of the Reaper War... and the details are very, very sketchy because another catastrophe that happened within that 600 years wiped out a lot of the records.  Regardless of how Scott ends the tale, Shepard is more than 600 years dead.

Perhaps "our galaxy" now refers to Andromeda and not the Milky Way.  From the image, we are certainly not standing on earth.