The "SMWAskAPI" extension adds an action to the MediaWiki API, "ask", that lets you call SMW queries via api.php:
I didn't think such a thing was necessary, since the Special:Ask page basically functions as an API already, if you use the query formats "csv", "json" etc. But I was convinced recently that this is in fact an important feature, for two main reasons: the API makes it easier to create queries, using the "...fm" formats, like "jsonfm"; and various libraries for running MediaWiki "bots" are configured for calling api.php specifically.
Any thoughts, then, on adding this code directly into Semantic MediaWiki? I know there's an overall goal to try to make SMW as small as possible, but this extension's code is pretty small - here's the main body of code:
..and its function certainly seems to fit in directly with SMW's core functionality.