Here's a quick audit of potential issues/blockers for OOJS migration:
Elements in mediawiki-ui that are missing in OOJS UI:
* stackable "block" buttons (needed for MobileFrontend)
* big buttons (used by UploadWizard)
* large inputs (used in Flow)
* anchors (used in MobileFrontend)
Elements in jQueryUI that are missing in OOJS UI:
* datepicker (used by UploadWizard)
* multi-select (used by CentralNotice)
Styles which do not match between mediawiki-ui and OOJS UI:
* constructive, destructive, progressive buttons - Which styles do we want to use?
* frameless constructive, destructive, progressive buttons - Which styles do we want to use?
* disabled buttons - The disabled buttons in OOJS UI are difficult to read. They should probably adopt mediawiki-ui's disabled style.
* standalone icon buttons - much smaller in OOJS UI, we probably need two different size options.
Can't tell if styles match due to OOjs living style guide entries that aren't actually living (uses screenshots instead):
* ButtonGroupWidget
* PopupButtonWidget
* ButtonInputWidget
* FormLayout
* PanelLayout
* Dialog
* ProcessDialog
* MessageDialog
Kaldari