So something like Arcana?
Honestly, that sounds like way too much work. I mean, look at Mage. That system takes up, like, half the book. *goes and checks* Yep, that's actually right. 180 pages of a 400 page book. Doing a system anything like that would be just too much for a part of the game that not every character would have.
Besides, "two-dot effects along the themes of endurance and protection" are already a thing. They're called Auxiliary Legacies.
I've been assuming that Sorcery should count. And if it doesn't count, then we should remove it from the "core dot" dynamic. Because otherwise, any character who put starting dots in Sorcery wouldn't get their Unique Legacy.