I'm using it from time to time. A lot of consumer equipment nowadays can only be operated with Android and iOS apps. For all those things I need WSA the Apps are off course not available in the official Amazon App Store, so i had to manually download them from f-droid and side load them with ADB.
I can see why WSA is not such an often used subsystem.
Edit: It was not f-droid, they don't provide APKs for copyright protected apps. It was shady mirroring websites that re-upload APKs from the Google Play Store. (downloading and installing from those sites is legal where I live).
I can see why WSA is not such an often used subsystem.