I would want to propose to add a type to indicate the content is contained wikitext, instead of a arbitary string. This could help VE to display a visual editor for those fields instead of showing the wikicode directly. This can't be done on "string" types as it's not certain they contain real wikitext. If the parameter is only to contain a single template invocation of a specific type, then perhaps a type "template" and a pointer to which template.
Version: unspecified
Severity: enhancement
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=52652