Thanks for asking! My initial answer is that these packages are not supported by Tectonic and are not going to be, because as I understand things, they are beyond its scope. The goal of Tectonic is to turn (La)TeX documents into PDF and (one day …) HTML files. On the other hand I believe that MetaPost and Asymptote are similar-but-different tools for creating graphics figures. I have never used these packages, though, so maybe they are involved in (La)TeX document processing in a way that I don’t understand!
You could certainly imagine applying the Tectonic approach to MetaPost and its derivatives, but this project is already extremely starved for developer time so the focus is very narrow right now.