This probably goes without saying. I would imagine this is more difficult than it sounds.
Maybe Storj could help with this, somehow connecting the users account with their own Storj address, not quite sure how but it would be cool to have a few more advanced features in future versions.
Then there’s the subject of group chat, but that maybe a whole new conundrum in itself with permissions and who’s identity the group would belong to…
Would be great to open a dialogue about attachments and group chat nonetheless.