From a roleplayer's view I'd love to get this too so we get the possibilities to share our clothes information or build a kind of background story etc.
From the addon's dev view I'd love to get this too so we can share our skills, champion point information etc. somehow to group/guild members or give advices somehow.
The negative aspect:
One could maybe somehow start "mallicious" stuff by sending a link which will trigger something in an addon, like "if you click this link the addon will destroy your gear"
This would also be able to do right now so it's not something what addon devs would do. So no worries.
@Zos:
If we can find a good way to do this I'd love to help testing etc.