They haven't announced any concrete timelines that I've seen. The last update I saw was about a week ago, in the thread about R3 questions, where this was said:
I'm thinking that they're focusing in the move to only serving ISRG Root X1 before they focus any effort on ISRG Root X2 and ECDSA signing (thus "still a while" being the answer), though that's just a guess on my part.