Yup, several companies are doing them now. The Bitubo kit should bring my up to essentially equivalent performance to stock RSU cartridge forks, with an appropriate spring. It's pretty much entry level for this sort of thing.
http://database.photozac2.com/bitubo...ridge%20&-Find
They do a more upscale kit, but that's meant for bikes that are already cartridge.
http://database.photozac2.com/bitubo...artridge&-Find
Traxxion will rebuild forks to cartridge, but they had never done a ER before and took a while to get back to me. By the time that they did, saying that they'd make my ER their first, I had already ordered the Bitubo setup.
WP does the pressurized fork setup also (2nd from the bottom).
http://www.wpsuspension.com/products/Race.php