Good IDE integration convenient for everyone but especially helpful to new contributors who are not experienced coders - they have to learn a thousand new things from code review / distributed version control workflows to security back practices, and if we can avoid adding "learn how to tweak your IDE configuration" to that pile, we can make the learning curve significantly smoother.
A well-integrated IDE would
- ensure that the right coding conventions are followed
- do some of the CI checks in a much more user-friendly way (banana, autoloading etc.)
- provide docs / typing / code completion / clickthrough navigation for systems which IDEs cannot figure out by default (e.g. hooks, global variables, extension-provided services, ResourceLoader modules)
- maybe show docs/help from mediawiki.org
- maybe warn when some MediaWiki best practices are not used (e.g. extension with PHP endpoint)
This does not mean that MediaWiki would be optimized to work with one IDE to the detriment of others, but it's nice to have a default.
PHPStorm integration already seems to have some momentum behind it, but which IDE we focus on is secondary to agreeing to focus on a single one.