Stay tuned. This part of DOM is currently under in review/testing stage. All editable fields in File Info dialog would be readable and set-able. That is for only categories: basic, origin, and IPTC (without an IPTC extension).
For raw XMP data… it will take longer since XMP is not unique to Photoshop but universal for multiple apps so it makes sense to have the same API in all apps.
Creation/modify date would be probably responsibility of file system module. Not sure about the possibility to edit it.