I'm not sure that "APIs" is much more narrow. I guess it could mean focusing more on how to improve moving data into and out of the wikis (distribution) rather than the business cases for doing so (analysis).
One topic that could be discussed both broadly and in depth would be bulk data dumps. This is an area that @ArielGlenn works in heavily and was discussed in the 2015 conference. I know that discussion lead to creating a phabricator project. Maybe there are topics in that area that are ready for additional discussion or evangelization?
Another general topic that crosses over a bit with the topics of code quality and future user interface enhancements is ensuring that all new business logic is available via the Action API or other externally automatable means. If we could make a collective decision that a SpecialPage must just be a user interface over an API that can be manipulated programmatically both inside and outside of MediaWiki+extensions then we would be turning a corner towards the possibility of radical new user interfaces (single page app, service workers, rich desktop/mobile apps).