The author of the blog produced one of the first online courses in AT and is active on twitter. When that launched, he was the first person I saw talking about it a lot online.
Meditation/mindfulness was growing in popularity in the 2010s and this stuff is just further along the tech tree. It was already well known with actors but the cross-over with meditation-like practices is pretty obvious if you look into both.
The (post) Rationalists you mention are mostly exploring technologies/methods around the connection between mind/body/emotion. There's no single figure pushing it along.
[1] https://en.wikipedia.org/wiki/Alexander_technique