The linked post was about Evan's side project, but within Figma, all of that is indeed possible. The glyphs are transformed into vector networks[0], which has a fill pipeline that supports transparency, gradients, images, blending, masking, etc.
+1 from another Figma engineer who happened to work on the text engine back in the day.
I think that Evan generally wrote code that was as simple as possible — there was no unnecessary complexity. In this case there indeed is some inherent, unavoidable complexity due to the math involved and the performance requirements, but otherwise I found our text rendering pipeline very understandable.
[0]: https://www.figma.com/blog/introducing-vector-networks/