The FormatValue API module should work simmilar to the ParseValue API module. It would expect a DataValue (in JSON format) as the input, along with an (optional) data type identifier, as well as the desired output format (plain text, wikitext, html, etc).
The FormatValue module would then find the appropriate formatter, apply it, and return the resulting string.
Implementation note:
FormatValue can probably be implemented in the DataValues repo, but should provide hooks that allow application specific data types and formatters to be injected.
Version: unspecified
Severity: major