It's taken long, and we really appreciate your patience. We have chosen to use a modified MAME licence first. We really encourage you to ask us if you feel you need the source licensed under a different licence.
The release currently has two forks, one for the main release and the other for the ports. A later release might merge both, but we felt it was more important to get it released instead of further polishing it.
Enjoy. If you like it, please consider donating. Thanks!