Since I've started to port Cura to PySide2 (I know it isn't ready now, but was interested in your progress), I found that QMimeDatabase is missing.
I couldn't find a ticket here for it, so here it is
|For Gerrit Dashboard: PYSIDE-458|
|182669,5||Add QMimeType, QMimeDatabase to typesystem||dev||pyside/pyside-setup||Status: MERGED||+2||0|
|184538,3||Add since attribute for QMimeType, QMimeDatabase in typesystem||dev||pyside/pyside-setup||Status: MERGED||+2||0|