I think anyone considering a new tandem frame for loaded touring owes themselves a serious conversation with Rick Jorgenson at Bicycle Engineering in Davis, Ca. Get what you want and need rather than "customizing to the extent possible." Purpose built and fitted custom racks can make a big difference. Others with "real" touring experience to consider are R & E in Seattle, Blinkey in Phillie, and True North Cycles in Ontario.
Our current touring ride was created by Dennis Bushnell just before he became head builder at R & E awhile back. The initial request for clearance for 700 x 48 tires with fenders in 2004 was met with laughter in Eugene-"we CAN'T do that"! Dennis said "sure, send me a tire so I can get the fender line right". Comfortable AND rock solid with the kitchen, bath, and laundry sink loaded up. If we stay young enough to think we will get another loaded ride, the most likely change might be 26 inch wheels to fit in the S & S shipping boxes with less hassle.
Look past the ad copy, much as the bike industry wants loaded touring and particularly TANDEM loaded touring to go away, it is still out there to be had.