A simple solution of something like +1 point of uncertainty (1/3 of a point of sigma) per day would be a good idea imo. https://forum.faforever.com/topic/2767/rating-sigma-should-increase-over-time?_=1652198278795
(Note that 1 point of uncertainty per day is an arbitrary example; the point is that rating sigma would increase by X every Y period)

Also, the league system doesn't solve the problem for global rating, and unless it does something like increasing a player's sigma, I don't see how it really solves the problem for matchmaker ratings either. After not playing in a particular queue for a long time, a player could be a lot better or worse in that game type, and their sigma should be higher to properly match that increased uncertainty. The increased sigma value would allow the player's rating to more quickly adjust and would yield fairer/better matches faster, on average.

the initial formula is just an example indeed,
some community voting can be organised to get the required numbers or something that is close to what the majority is willing it to be

Uh no don’t do a community vote on the best way to structure a statistical distribution system lol

A rating decay with a lock on how much it can decay seems like the optimal solution. With the data they've got they could figure out the optimal formula over time.

In general, and it might take 5 games to start the "de-rusting" process, I don't think people degrade more than 200-300 points

So there's no point in having rating degradation beyond that

Someone who accomplishes reaching 1,000 points in ladder rating can probably come back to the game 20 years later and still play like a 700

Imagine the games that you used to play 20 years ago. How hard would it be to pick them up again? If you used to speedrun Goldeneye N64, I'm not saying you could speedrun it, but I doubt you would have trouble beating the game.

An RTS isn't going to be all that different.

Since the decay is only going to be a modest amount, why bother at all with any rating decay? It would be a lot of work to implement and test and in the end there's barely any point. It would only take around 10-15 matches for the person's rating to become correct. Their actual skill would go up during those 10-15 games and their point rating would drop during those matches until they became about equal.

It's a minor problem that requires no solution.

The important question would be: would adding a rating decay system encourage players to come back to the game? Probably not. So why bother?

The forum really is just a recycling of the same 10 ideas over and over every few months. I'm down to play some ladder in 19 more years and see where my rating ends up. Then you guys can be sure exactly how much decay to implement.

Instead of having players rating degrade over time why not have the same rating colour system for new players (you start off gray and slowly change to white). But instead of grey have another colour (maybe yellow ?), so the longer a player is away the more yellow their rating becomes.

Prismata has an interesting approach to this:

That leaves 90% with a permanent vacation penalty

For Prismata I'm sure it's more like 99.9%

But I'm just providing an example of their system, not saying we should copy it exactly.