Note that Agenda can already handle a lot of links. Drag an email in, and you get a link to the email. Drag a file in, and hold CTRL as you drop it, and you get a link to the file. Same will work with other apps that provide links (URLs).
The discussion here was more about linking in Agenda itself. You can already do that, but some people want to have a backlink created when you make a link, ie, a two way link. We have some ideas about that …