Problem: The new 2017 beta wikitext editor has a decent visual preview feature, but it lacks some information like templates used in the preview and parser profiling data, the latter of which has some useful information like the amount of PEIS used.
Who would benefit: Editors who are trying to analyse things like PEIS on (large) articles without needing to switch out of beta.
Proposed solution: Add an icon that can be clicked or hovered over to display the data.
More comments : If this could somehow be implemented for the VisualEditor that would be nice as well, but something tells me the lack of a preview function for the VE would make it harder for my proposal to be worked into it.