Remailer message bundling

If each remailer encrypts outgoing traffic with its (immediate)
recipient forwarder's public key, then several outgoing messages
headed in the same direction can be bundled together, obfuscating
further the message identities.  No need to have 1 message in ==> 1
message out, with or without delay, reordering, or whatever.  But
maybe everyone already thought of this.