Build more data source connectors (it's all bonus)
The two existing data sources are:
- web scraping a french website
- calling a professional book data provider, french too, by SOAP (a GET with the right headers)
Everybody's welcome to write a web scraper for his country.
Google books or ISBNDB don't have enough data for professional bookshops (not enough books, no price, and no professional data), but maybe would they be enough for individuals.
Look at the Amazon API again too.
That's all bonuses, not a priority.