spoilers all through this, you've been warned-
Well, after over 300 hours of tinkering and playing about, I finally decided to ride out one of the obvious paths to end the story.
I had planned to finish the Railroad synth-escape plan, but what that turned into was basically a.) go blow up the prydwen and then b.) kill off a ton of people in the institute and then blow it up too, with the ending being "the railroad wins".
Given the game's varying options for attitude in dialogue (kind, mean, sarcastic, etc), I had hoped for a possible blended outcome.
Then I looked at how many hours I spent finishing up that one story ending, and decided to just go read the wikia on all the possible endings.
There really isn't a "free a bunch of synths, and then in your role as leader of the institute, change their attitude about synths and their freedom".
Bummer. I didn't hate it, but I was a little surprised that there was no way to have a sort of happy ending.
And the BOS were a bunch of arrogant dangerous warmongers, but even they had hints that they might be won over to cooperate in some ending where we don't kill off half of the population.
But then again, war... war never changes.
What did you think about the ending?