StevenG, on 2015-August-06, 10:36, said:
The question for me is whether it will get rid of the big decks around rank 20 by encouraging them to get to a more appropriate rank, or if it will make those ranks harder by encouraging people to play ranked who normally don't.
We'll have to wait and see - my guess is no for two reasons:
Currently people farm portraits at rank 20 (gold-farming is easiest in Tavern Brawl) so those rewards won't change their incentives (whereas discounting ranked wins at lower levels would).
It seems likely the rewards will be based on peak performance (apparently people camp at certain ranks due to ladder anxiety), so if you really wanted to be an ass you could climb to rank 5 (maximum rewards according to a later twitter from Blizzard), then drop back to 20 to continue farming.
As an aside, getting more people to play ladder will make it easier - it's not as though there are a lot of legend players who stopped laddering because no rewards. More likely there are people who mostly play casual/arena/TB and thus will be worse than current ladder average.