One of the first points in the article was that wasm became widespread enough that they could migrate them performance critical parts to C++ and the rest to typescript. The necessity for skew simply wasn't there anymore

We actually recognized that Skew had become a liability years ago, and Evan worked on a proof-of-concept to remove Skew around ~2020. But as described in the article, benchmarks showed that performance would have been severely impacted (mobile Safari was an especially big problem). The rewrite only became possible once mobile WASM was performant enough for us to move the hot parts of our code to it and we had enough engineering resources to do it safely.

It does smell like someone's pet project. I'm wondering what the folk at Microsoft had not figured out, that they indeed had at Figma. Typescript is open source, so why wasn't this optimisation just made as a contribution to Typescript at the time?

Also, was Typescript really as claimed in its "infancy" at the time mentioned in the article? They didn't mention a particular year.