Per the documentation for QuickInstantCommons:
The QuickInstantCommons extension is a performance optimized version of $wgUseInstantCommons.
It shouldn't provide loss of functionality, but rather improved performance. We should consider replacing InstantCommons (which we've always known has performance issues) with the viable better performant QuickInstantCommons extension.
We could even hack a way to enable QuickInstantCommons via Special:ManageWiki/settings if we want to keep it enabled in the same way, by creating a variable $wmgUseInstantCommons which enables the extension.