with the help of other developers, I successfully got a Raspberry Pi with the Openlabs 802.15.4 radio adapter  working as a 802.15.4 and 6LoWPAN border gateway. A border gateway running Linux should allow adding more gateway and translation functions useful for the IoT.
The configuration process, including example. can be found on the wiki  and is tested with the Linux configuration on that page and current master of RIOT.
Thanks to Alexander and the rest of the Linux wpan community in #linux-wpan on Freenode and to Martin for building the Pi images.
 http://openlabs.co/store/Raspberry-Pi-802.15.4-radio  https://github.com/RIOT-OS/RIOT/wiki/How-to-install-6LoWPAN-Linux-Kernel-on-Raspberry-Pi (all the way at the bottom)