The new ranked play reward system seems like a missed opportunity to me.
Rather than getting a card and some dust, I'm much rather get an improved card back for the month of ranked play based on my highest rank. For example, Rank 20-16 may get the basic card back for that month. Rank 15-11 would get the basic card back with a bit of animation or gilding. Etc etc. And Legend players would get the most awesome version with crazy animation, etc.
It would be a great way to show - hey I kicked a$$ in Season X. And it would motivate me more than the current system to really tryhard in ranked. Plus it gives rank more flavor rather than try to just copy the arena's reward system.
They should just make another chest for legend. Rank 5+ and legend is at least 150 games apart for average legend player i would say. Rank 16 to rank 5 is doable usually in one evening if you are not doing it day 1.
But to the topic, golden cards are nice reward for free to play. You have the legendary card back already, but i could see 2 versions of cardbacks each season, static and animated (same as golden and normal cards).