Frameworks seem to be handled a little… differently… compared to platforms and other bits of PlatformIO. They are hosted on Bintray as downloadable packages, and in essence are just packages from the various source frameworks packaged consistently, all in one place on the Bintray CDN. However, as you’ve spotted, there are a few tweaks and extras.
framework-arduinoststm32 package is here : https://bintray.com/platformio/dl-packages/framework-arduinoststm32 … but it’s not a repo as such you can contribute to. Probably best to open an issue with the suggested changes on the platform-ststm32 repo, and point out that you can’t do a PR because the framework extras aren’t tracked.
Or am I understanding that wrong @ivankravets @valeros ?