A couple of comments....
While not a carbon fork, Steve Rex in Sacramento (
www.rexcycles.com) has built a number of steel forks for Glenn Erickson's dual-disc road tandems that are about the same weight as most regular steel forks but that incorporate a right fork leg-mounted disc caliper and an unique, extra-wide crown design that allows the forks to accommodate a 203mm rotor. The crown also incorporates a caliper brake bolt hole in the even that there is ever a need or desire to run rim brakes instead of the disc, e.g., field-repair while touring, etc...
Dennis Bushnell is also building a tandem fork that can accommodate a 203mm disc rotor with right & forward mounted caliper. Rather than the somewhat artistic looking Erickson design, Dennis' forks are reminiscent of Cannodale's Fatty with with an extra-wide crown.
On rims, the only thing that you might want to consider is the use of an off-set rim from Ritchey "Trekking OCR" for your front wheel. The OCR rims use steeper spoke angles but eliminate most of the dishing that a normal rim would require when used with a disc hub. You're limited to 32h, but given your team weight of 330lbs a 480g 32h front rim is more than adequate. Velocity also makes an off-set rim -- the Aerohead OC -- which comes in a 36h version; however, at 400g it's not nearly as robust as the 32h Ritchey and it's also a bit more narrow (20mm vs 23mm).
As for James & Jules front disc mishap on their Custom 26" Calfee Tetra Tetra Enduro, the root cause is believed to be the orientation of the opening in the drop-outs. The skewer coming loose was believed to be a by-product of the braking forces working against the axle which -- if James' models are correct -- was only held in place in the front fork by the skewer instead of having the braking forces from the crown-mounted brakes pushing the axle into the closed end of the drop-out. Thus, a bolt-on axle may or may not be any more effective than a stout steel skewer applied (perhaps a locking skewer) with sufficient pressure in the event nothing else is done to beef-up the drop-outs, e.g., changing their orientation or the caliper mounting ala Erickson's design.
Back to the basic issue of front discs brakes on road tandems, IMHO they are still in Beta test-mode. Anyone using front discs needs to recognize that there is very little long-term field data available on fatique life for forks and wheels being used with the Avid or any other type of disc brake caliper. While there is a wealth of information available from the field on off-road tandem use of disc brakes, that information is not directly transferrable to the road tandem applications as the method of use and conditions are vastly different in terms of the physical demands placed on the equipment. Thus, I still maintain that discs are not for everyone and, more importantly, anyone using them should be very attentive to preventative maintenance and inspection of their brake calipers, rotors, pads, hubs, wheels, and forks. Be mindful to look for stress cracks and to follow-up on any unusual noises that you hear when using your brakes. A loose brake rotor attachment bolt can wreak havoc on your calipers as can a cracked rotor. Stress cracks around spoke holes in a hub or rim usually appear well in advance of any actual flange failures or spoke pull-throughs -- noting that these types of failures happen on tandems that don't have front discs.
Finally, with regard to Avid's "tandem-approved" brakes. Bear in mind that the approval and warranty coverage is limited to their use as primary brakes (not drag brake use) and with the 203mm (8") rotors (which is what comes on the C'dale tandems) not the 160mm rotors. The preclusoin of drag brake use is why Co-Motion will not sell its road tandems with enough brake cable fittings to allow the simultaneous operation of the disc and rim brakes.
Bottom Line: Disc brakes are not for everyone! Please do your homework and make an honest assessment of your brake equipment needs / expectations before making a 100% commitment to disc brakes. Even then, strongly consider making sure you can retrofit rim brakes (caliper or cantilever) to your tandem in addition to the disc brakes because needs change.