Thanks for your question. We do have plans for this feature. It is in our backlog and likely to be completed during Q2 of this year.
Product Engineer | Open Data
I've been able to program around this issue by including an HTML hyperlink tag in the service item description to the HTML, and I'm sure it would work for XML, version of the metadata that is saved on our servers. For Example:
<a href="www.linktomymetadata.com" target=_blank>For metadata, click here</a>
Its at least a stop gap until ESRI gets their metadata engine for OpenData up and running.