Earlier quoted context omitted.
There's still time to open source it. I'm confused why they don't, at this point. Well, not that confused, I guess it ties in to Windows quite a bit and it's probably not worth it for them. Still I hope they do it.
I do not think it is trivial to port EdgeHTML. Don't forget it is a fork of Trident with the legacy parts clipped away and some cogs polished, replaced or added. Not meant to run multi-plat, not even meant to run outside Windows 10.
But open sourcing it for the sake of practical domain knowledge, if not history, would be good.