Is there any reason not to enable https://www.mediawiki.org/wiki/InstantCommons by default? The docs don't show any. At least non-standard configuration for cache etc. can need some adjustments, AFAIK, but it seems it mostly "just works" as expected?
Nemo
P.s.: I had already asked at https://www.mediawiki.org/wiki/Talk:InstantCommons#Enable_by_default, probably disappointed users would have shouted their NO!