In general, I really like disc brakes, and at the moment i'm looking to build up SS bike using a TT-base bar on an MTB frame and mtb disc wheelset. ( Quirky, but hey, aint that what SS is about??? )
Whilst it would be simple to use mechanical calipers and TT levers, the thing which cheeses me off from experience is the static inner pad on mech discs. Hydraulics and their opposing pistons just seem so much better in terms of clearance and grabbing the disc without twisting the rotor.
So instead of having a master cylinder in the lever and a slave chamber in the caliper pushing the pistons, why not have a cable pull lever on the caliper itself acting on a chamber ( like the current hydraulic levers do ) which then pushes directly onto the pistons. Would be simple to bleed effectively a single chamber. Would simplify the hydraulic side of things ( if making the calipers slightly bigger ) and you could get super light levers.
Personally, I think there is a market for it. The ability to use any cable lever ( TT, Road STI, V brake etc ) , but with the benefits of hydraulic caliper pistons.
Or is that fairy land dreaming ???