I have started an RFC, putting down my initial thoughts on how to make Wikidata API more seamless with the core API.
The goal is to minimize execution time, bandwidth, and server load, while making it play nicely with the rest of the action=query, allow for continuations and multi-values data request capabilities.
For now I only looked at the wbgetentities, but the RFC will be updated with the other modules. Please let me know what you think.
http://www.mediawiki.org/wiki/Requests_for_comment/Wikidata_API