See PHI1343. An install would like support for "date" and "remarkup" custom fields to be exported in Excel/CSV/etc.

• Exporting "date" fields is likely straightforward, and the existing PhabricatorEpochExportField should work well.
• Exporting "remarkup" fields is possibly a little trickier. We currently export "text" fields using PhabricatorStringExportField. For CSV and Excel, we should likely just do this for remarkup fields, too. However, for JSON fields, we should possibly export array('raw' => $field_value) (similar to how the "description" field is exported in Maniphest) to future-proof this against wanting to export alternate renderings or formats (e.g., exporting both the raw remarkup and a human-readable text rendering)? On the other hand, if you really care about rendering behavior you can (and probably should) just use the API. At the end of the day, this feels fairly YAGNI to me and we should probably just map "remarkup" to PhabricatorStringExportField and call it a day.

See D20316 for a recent similar change.