I dislike the brawl format for draft. I find it tedious. Rather you fight one match at a time (like ranked) from a pool of people with similar records.
On topic of people keeping contents from packs, that will devalue packs significantly. (Infinite print basically.) So I think it would be better if people don't keep the cards outside of draft. (Hearthstone Arena does this.) Plus, cheaper entries as a result so you can play it more.
I think a cheaper Phantom draft idea is a great option.
I dont think this would devalue packs, because these would be the same as the general sale packs. It shouldn't add supply, but just be factored into the regular release. If they wanted to do Untamed or previous formats it would be pretty expensive, so maybe those could be phantom style.
My worry with Ranked play style games is that it ends up just being the luck of the packs, versus some deeper team building strategies. I also think utilizing more cards would be better for the game. Thoughts on those issues?