Allow simple validation rules to be defined for each custom field. To start with, just forcing numeric, date and string would be good. Validation closures could come next.
A filter on each one would also be good so that any custom validation or mapping rules could be used.
Use the new v2 REST API (WC 3.x) instead of this plugin. It now does everything this plugin does out of the box. The README gives some examples of how you would manage the metadata fields.
Allow simple validation rules to be defined for each custom field. To start with, just forcing numeric, date and string would be good. Validation closures could come next.
A filter on each one would also be good so that any custom validation or mapping rules could be used.