I would say that’s a different feature they are asking for, isn’t it?
What I think @Dara is asking for is for the possibility to access the attachments when offline, not modifying them. That could be accomplished caching them on the client, as it’s done with the items themselves.
I also guess that this should be configurable per client, as with very big attachments, this could fill the disk quite fast. What do you think @kspearrin?