and sooner or later a significant number of those in-house LANs will 
be connected to the internet, because the convenience in doing so 
far outweighs the risk.  
and if you think that the LAN will be behind a firewall, think again.
every new internet protocol requires authentication, the old ones
are being refitted to support authentication, and the digest framework 
allows single sign-on.  there will be far less need for a firewall, 
than there is now, and firewalls are a poor mechanism for access 
control anyway.
it is really starting to sound like folks want IETF to bless the
practice of making limited-functionality devices so that those
devices don't intrude on the markets for more expensive devices.
Keith