If we take it from now, 50 years gets us to 1969, right in the mod-era Diana. Maybe it's a reference to that?
One possibility is that Diana knew she needed to get Grail away from the corrupted Amazons for Atlantiades to be able to do their thing successfully. But if that was the reason, it sure wasn't apparent on the page.
In a way, the pacing of this arc feels a bit off. The setup (Xermanico's opening) was great, but the battle was muddled and there were elements of the resolution that felt unbuilt.
I liked Maggie more when she was more Etta than Etta, back when we first met her and in the Rockies. After she got the sword, she lost that romantic and positive personality.
And yes, more Amazons, perhaps especially getting into Diana's and Kasia's relation.