Earlier this month, LoL patch 10.13 launches.
That's according to a new 2020 League of Legends patch cycle is on Wednesday, June 24, 2020 – and its scope will "expand" as it goes on.
Germain says you'll know the experiment is live in your region if you get a "one-time notification" pop up during Champ select.
The dev explains it's launching the first experiment – Champ select muting – to see if it "leads to changes in behaviour related to negative chat in champ select and in-game", while the second is to "gain a clear understanding of how often different types of negative behaviours occur in Champ select, and the different impacts they have in-game (chance of winning, rate of in-game reports, etc)."
https://twitter.com/MarkYetter/status/1275085692171780098
Once the latter experiment is up, the post says, Riot will use the data it's gathered to work out any investment in a "penalty system" as a second iteration of the feature.
So, with patch 10.14 due to launch on Wednesday, July 8, 2020, and the following a fortnight after, it looks like we can expect the experiment to be running roughly between June 24 and July 22.