It would be cool if you eventually added Traditional characters as an option. It would take almost 0 effort to better serve the 1 million foreigners living and/or working in Taiwan. Obviously it would require more effort to change vocabulary words around from their Mainland to Taiwan counterparts (For example, 計程車 in Taiwan vs. 出租车 in the Mainland) or re-record vocabulary words to remove the Beijing -r from... everything, but swapping out characters would be a snap.
You can already do the course in traditional Chinese with this extension.
As for Taiwanese, Cantonese audio...watch this space.