Hey,
Checking such extension status is essentially solved by dependency management. And dependency management is solved by various tools, the one being relevant to MediaWiki and other PHP projects being Composer [0]. In fact this capability already exists for several extensions, though there is no nice GUI for it yet. An example of such version checking can be seen at [1] which checks if the versions required for a component are up to date with the ones it provides. In that case the thing being checked for out of date dependencies in a component itself, though the exact same code can work for a wiki. Some relevant pages on the existing support are [2, 3, 4].
Implementing the ideas I outlined in [4] is not terribly difficult and will result in very powerful capabilities. Or rather, it will make them a lot more visible and accessible, which will then likely result in wider adoption of the underlying paradigm (dependency management) amongst extension authors. I estimate that building a working prototype can take as little as two days, as indeed most of the groundwork has already been done [5].
That is in contrast to scraping things of gerrit, or relying on info on MediaWiki.org being comprehensive and up to date, combined with building an own solution. I anticipate such a solution to be way less powerful, much harder to maintain, being rather brittle, not being interoperable at all, and harder to create in the first place.
[0] http://getcomposer.org/ [1] https://www.versioneye.com/php/mediawiki:semantic-mediawiki [2] https://www.mediawiki.org/wiki/Composer [3] http://www.bn2vs.com/blog/2014/02/15/introduction-to-composer-for-mediawiki-... [4] http://sourceforge.net/mailarchive/message.php?msg_id=31680734 [5] If you think I'm full of shit, throw me 2k USD and I will prove you wrong
Cheers
-- Jeroen De Dauw http://www.bn2vs.com Don't panic. Don't be evil. ~=[,,_,,]:3 --