That character moment will still need to progress the story. Mind you that Ashoka is likely much more skilled in the Force arts than Kanan and Ezra could learn a few things from her. I would assume Vader would kill her at some point, though I now it will pain a lot of people when that happens (including Filloni). But she'll eventually be a dangling thread that needs to be addressed before Luke finds out about Vader's past. While it would be interesting to see Ashoka interact with Luke and perhaps train him a little before he needs to head to Yoda, I don't think we will get that moment. One it makes the universe smaller, two, Luke still knows too little about his father, and Ashoka knew "Skyguy" rather well.