I am glad someone posted this thread here since I saw that email come through a few times over the past few months and thought it was spam, a scam, or another test/experiment that was being ran (i.e. David was testing SubStack a while back). I didn't give it much thought until recently. You can't ever be too careful these days.
I am still largely undecided on the move to the new platform. I have mixed thoughts. There's definitely been, and still are, issues both in terms of communication and coordination in rolling it out to the community. The 75% price savings is quite nice though, that's very much appreciated and more inline with the current reality. The overall topics/groupings seem more relevant in the new platform, though that could just be what's in the with the times.
As for the platform itself, well, it's definitely more modern than XenForo (the underlying platform used by GTDConnect) that's for sure. It is not a forum platform, which is different. I am not sure it's better or worse, just different. Personally, it's pretty clear that the MN platform is not conducive to effective communication or learning. It's really geared more towards the "social media feed" consumption mentality, which is a bit of a weird choice given the GTD brand. I could be wrong though and just not experienced enough with it.
I am sure there are larger plans and more details to work out. However, at the moment, there's no reason to use the new platform in favor of the current one. I am largely ignoring the new one for a few reasons. Mostly since there's no threads to quickly gauge things and see a larger swath of information (again, it's geared for a social media mentality by having each entry be obnoxiously large "cards"). More deeply though, there is no value available in the new platform. Nothing has been cloned over to it from the current one. It's, for all intents and purposes, empty and lacks usefulness that the current one has built up for 20+ years.
I have the new GTD Connect platform on my "wait and see how it goes" list. I will say this though: not having any plan to clone content over to the new platform (as I haven't seen or heard anything regarding such) while just shutting down and losing the current platform, at any rate, would mean effectively ending GTD Connect. At that point, it would make Reddit a more effective community to then join and discuss GTD (which let's be honest ... Reddit's not a good thing per se).