It would be handy if there was a form (like config_flow async_show_form()) that allowed file upload for use in a flow. The front-end there could provide a drag&drop handler and a regular button opening a native file browser modal.
This could be used for integrations currently still relying on yaml due to their non-discoverable / manual entity settings nature (eg. KNX) to set up entities from an elsewhere exported (eg. .xml, .csv, .zip, etc) file.
This is possible since a while now via a selector.FileSelector() 