I don't think that adding a whole parser function that can only draw an icon and add title attribute is worth it.
At least you could use jQuery tipsy plugin, that is bundled with MediaWiki and allows block HTML tags in the tips, as well as nested tips.
There is no need to define a parser function: a template and several lines of JavaScript code in MediaWiki:Common.js or a gadget will do the job.
Whether this is sad or not I'm unable to argue with but it is a no-frills feature that was born out of the necessity to display information within SMW (jQuery tipsy was evaluated and did not support the features required).
The #info parser is an add-on (not really necessary for core but it was introduced some time ago) with a low barrier for technical adaption and is more or less maintenance free.
If a user wants to use somethings else it is entirely up to him/her to do so or if someone wants to submit a PR to improve the #info functionality that would be fine as well but no core developer will spend any time on improving #info because it does what it should do, provide a simple "info" about an entity marked by an icon to indicate the severity.
