Wouter,
all your reasons aside you seem to have forgotten that no one else but you is going for the support tubes and with the exception of Phil's boat the ones starting to build right now are all stayed. I should also point out that the boomless rig was the idea of the people building the boat and they are paying for it, so I guess it's their choice.

BTW, your analysis of the small flap at the bottom is just plane wrong, I have recently done a lot of CFD work on just this subject for the A-Cats in the form of a mini sweeper (about 400mm chord) and it is extremely beneficial even without a seal to the tramp an I for one will be adding them to any design that the owner allows me to.

Cheers
RG