A no new players feast queue?

[Zojha]

But seeing as pretty much any other solo queue mode uses such a system[...]

To be fair here: League of Legends only has decay for platinum and up - gold, silver and bronze, so 90% of the ranked playerbase is unaffected - oh, and gold happens to be the rank where you get the Seasonal Skin, so the main reward for ranked. And I didn't pick the monthly active players as reference earlier at random - Rating decay starts at 28 days of ranked inactivity there. For Master and Challenger players (the top 0,05%), you need to play a game a day (though you can bank up to 10 games as reserve).

In fairness, their seasons last about one year. Our seasons last...three, four months? Divide the whole thing by 4 and you get to around 1 game per week - for platinum and above.

DotA2 IIRC has no rating decay and uses MMR as rating for ranked games. Overwatch I think implemented a rating decay recently - it's 50 on a scale of 5000 per week until you play one game. In their system however, decay won't get you below 3000 rating however, which is diamond for them. Starcraft 2 MMR decay used to start at 2 weeks of no game and was capped at 4 weeks or about 310 MMR - It also got removed entirely as of August 2015. CS:GO has no rating decay - it just gets hidden if you are inactive for a month (Admittedly, that information is shaky).

So with ~10 games a week, you're pretty much asking for the harshest rating decay in probably one of the the least competitive games out there. Just to put that into perspective.