Maybe Disney will make the original films no longer canon either, lol.
But yeah that's why I was assuming Ahsoka has to die, and maybe Kanan too, which would explain why the Alliance has such a hard-on for Luke. They saw what Ahsoka and Kanan could do and expect the same things from him. But yes, whatever plan Yoda and Obi-Wan have going on doesn't really make any sense. Obi-Wan should have been instructing Luke from a young age. Wasn't Anakin's age the main reason they didn't want to train him as a Jedi? I mean Mark Hamill didn't look it but Luke was supposed to be 19 years old in A New Hope. They didn't want to train Anakin, who was only 10 years old, but training a 19 year old is fine?
I mean that doesn't fit into the space fairy tale that George Lucas wanted to tell, but it damn sure makes more sense than just living in a cave and a swamp doing absolutely nothing until Leia desperately reaches out for help and by random chance the droids she sends, which used to belong to her biological father, end up being bought by the not really uncle of her brother.
I don't know if Ahsoka knows Vader is Anakin or not. Vaders identity doesnt seem to be common knowledge or Luke would've found out from the rebellion in Empire instead of from Vader himself. It would be better dramatically if she doesn't, as I see a Ahsoka/Vader duel in a future episode.
I'm pretty sure if she confronted him face to face, she would recognize from the force that he used to be Anakin. Obi-Wan recognized Vader's presence despite not having seen him in 19 years, and it's only been 15 or 16 for Ahsoka. You could maybe argue that Ahsoka hasn't seen him since his fall to the dark side whereas Obi-Wan had though.
Here's another thought, Obi-Wan is way too young in the prequels to have turned into a white haired old man a mere 19 years later, which is how much time supposedly passes between movies 3 and 4.