There is a curious phenomenon that exists when you take a look at the ladder league data: the 1800+ league basically has zero activity. As of the 27th, only 2 players with ratings above 1800 have played more than 30 ladder games over this month. Why is that?
I believe that it is because the incentives to play ladder are broken. A high ladder rating is valuable because it guarantees favorable seeding in tournies, which usually have money on the line. Inactivity guarantees this ladder rating will be maintained, while activity will run the risk of potentially lowering this rating.
As the title of this post suggests, I believe the solution to this issue is the implementation of some form of rating decay. Whether it is necessarily decay in the actual rating, or just the uncertainty, there needs to be some incentive to have people continue to play ladder. Back when I had played Heroes of the Storm, my rating would undergo a soft reset every 3 months - people who had achieved the top rating would need to play consistently to maintain that rating. This is the case for many other online games, and should be the case for FAF.
My proposal: add in a rating decay system based on a visible rating and an invisible rating.
v = Visible rating
i = Invisible rating
t = Inactivity tracker
v = i*0.96^t
Where t=t+1 for every month that passes without 10 games played and t=t-1 for every 10 games played.
It's a pretty simple and straightforward system that adds decay based on how long a person hasn't played for. This can go hand in hand with the new "divisions" system, which displays a visible division rank (visible rating) on top of the actual player rating (invisible rating), but also works directly with the current rating system.
A returning player should find that their rating rises quickly with activity.
This also fixes the issue FtX is facing with tourney seeding - instead of having to give completely inactive players a rating of 0, the rating system already accounts for the decay that should happen.