Much like the mailing list itself, the discussion here about potential migration just kinda... stopped.
It is not surprising. If you compare the discussion today, with the discussion in the past, then you note it is much different, than it was. And you also note, that people moved to other places. For example, there are IRC channels, there are GitHub discussions, and also note that the winter holidays are coming.
Another thing is that if you want to see new messages, then someone should accept them. Which means, even if there is some traffic, waiting to be published, you can see it a day or two later, because things are moderated.
Do we at least have some sort of leading contender or front-runner yet?
Not really, and there is another possible outcome: the list could just silently die, without any replacement. This is also possible, and this will not be the end of the world, because participants know their e-mails, and can exchange some messages directly, without any list, and another list can be formed from scratch, when there will be a need for that. Because if there is little or no demand, then it is normal to have little or no supply.
I got the sense that it's a time-sensitive matter
It is not. It is e-mail based, and also moderated list, where it is normal to post something, and have your message rejected, or published two days later. It is not like this forum, where you write a post, and where it is immediately fetched by some bots, and where all statistics are recalculated based on that, and where people can see the first version, even if you edit or remove it.
Have they said anything about this matter?
Not really. I don't think there is anything under the hood, that you cannot see publicly. I think the main idea is to let it die, and create something new, only if there will be any need to do so. And I think it is a good approach, because there are many ways to communicate, and because if someone would want to talk to any participant on the list, the e-mail address is usually public, so if you want to know, what John Doe thinks about that, then you can just ask him directly.