A new feature was added to Gmail Labs that will show a previews of photos or videoes in email messages in the Gmail web interface. This will happen when only a link to is included in the email. I tried this, and it works pretty well.
I wonder if a following version of this feature will present your email in a graphical view, based on the content either attached or linked to email messages, instead of a text based view of the email messages. This could be someing similar to Xoopit, but wouldn't have the security issues that I mentioned before.