Oh no, haha, I didn't mean for each and every roll, unconditionally! My main point was just that it should not be success or failure, specifically, that gives you xp for a thing, but rather doing the thing no matter the outcome.
What I would suggest for this here hack is to keep the milestones as they are written, but use them as keys instead of prerequisites, so that when you reach a milestone, you check it. When you have a set number of checkmarks, say five for now, you improve and get to pick a new skill. And erase all the checkmarks.
Add to this a checkbox for every basic move, because we shouldn't penalize characters who move outside of their career box.
I really think we shouldn't worry that much about characters advancing too easily. You have the potential for powerplaying in regular old AW as well, but in the five years since it came out, I have more or less never seen it become a problem. Sure, sometimes in AW someone might get two improvements in one sesh, but it evens out, since your highlighted stats change every session.
Besides, change and growth is fun! :)
Now, I'm not advocating highlights like in AW here, I think checkmarks would be better. I'm just making the point that easy growth is not necessarily a problem.
Unless of course it stimulates one-sided play too much, but both the checkmarks and the hightlights-from-other-players approaches take care of that.