If anyone is interested.
I made a quick and dirty tutorial, to set up up a headless instance of backdrop.
Since i had issues with cors i ported over the CORS module from D7 (i just changed he *.info file).
it is compatible to use the existing drupalgap/cordova stuff from D7 to build hybrid mobile Apps.
Instructions are here:
<<<<Outdated link has been removed>>>>
Hope you enjoy...