Oh. My. God. You win. You win Smutmas and the holiday exchanges and the fandom and the whole damned INTERNET.
You've managed to write across different generations and time periods, and weave it all together seamlessly. I'm completely floored. (Of course, I do have a serious weakness for the too-seldom-written Godric/Salazar, so... ::grin::)
The portrayal of Salazar and Godric's story is wonderful. The characterizations are fantastic, and the time period feels right. Here Hogwarts is not an anachronism, but a dynamic structure in its heyday. I love the feel of old magic, old rites, old traditions. And I love the subtle ways in which various events and views have become somewhat twisted and misunderstood or misrepresented over time.
I'm so impressed that you managed to write both Snape/Harry and Albus/Scorpius in a single fic in such a way that I could relate to characters of both generations. Typically I'm not terribly interested in the epilogue kids -- not because I have anything against them specifically, but because I'm most invested in the "original" cast of characters, and I don't like them being relegated merely to the role of "someone-or-other's stodgy dad" or similar. That didn't happen here, however; Harry still feels like Harry, and I'm still caught up in his story, even though part of the fic is from his son's POV.
Also, I have to say, I really enjoyed your characterization of Scorpius. He's perfect. He's adopted a lot of Draco's mannerisms, yet he's clearly not Draco. Really well done.
Seriously, can I flail about this enough? I don't think I can.