There's much more to making a leaf shutter work than putting a shutter in the lens, especially in an SLR. When you press the shutter button, the following needs to happen:

1. the shutter closes and cocks, while

2. the mirror swings out of the way

3. the dark curtain opens (the part of the dark curtain will be played by the focal plane shutter in a hybrid design)

4. the leaf shutter opens for the required time, then closes

5. the dark curtain (FP shutter) is closed

6. the mirror returns, while

7. the shutter opens again for viewfinding.

Simultaneous with the mirror and/or dark curtain movement, the aperture will be stopped down to the shooting aperture, the sensor will be cleared (if necessary) and the capture cycle started, then after the exposure and while other things are going on again, the aperture will return to wide-open and the sensor read cycle will be initiated.

This all requires a degree of communication between parts that isn't normally part of a small-format DSLR. Hasselblad has been (mostly) built around leaf shutters only (we'll discount the 1000 and 1600 as "prehistoric"); hybrid MF DSLRs such as the Phase One/Mamiya 645D and the Leica S have the complicated comms system built in. To see what's involved, you need to see an MF back mounted on a technical/view camera, where the triggering signals are usually passed through a Rube Goldberg chain of flash syncs (and there's not even a reflex mirror to worry about). Remember, too, that the metering system needs to know which shutter is in use in a hybrid system, and that the effective aperture for metering purposes will depend on the shutter speed.

So it's certainly possible, but there will be a cost. The extra mechanical complexity and timing issues will mean that frame rates will come down. Both the body and the lens have to support leaf shutter shooting, so gambling on a LS system means introducing both new lenses and new bodies (with extended lens mount contacts) at the same time, and with a large enough variety of lenses likely to suit the needs of flash shooters (or there will be a chicken-and-egg problem: who's going to spend the extra on a body with too few lenses, and who's going to make lenses for a body that isn't selling well?).

One could also argue that the need has largely been mooted by high-speed sync (or Auto FP sync, in Nikon parlance). Studio and location flashes that use IGBT or similar technology are also capable of supporting high-speed focal plane shutters; at least Profoto (with the B1 Air TTL), Elinchrom (the new ELC series) and Broncolor have mentioned that they are working on the problem and are likely to have working HSS solutions on the market soon, and one of the "overgrown hotshoe" makers already has an "HSS sympathy" mode (not TTL, but an extended series of pulses in manual mode). Given that the problem is being solved in other ways, there is even less incentive for any small-format DSLR maker to gamble on a new body-and-lens system than at any time in the past.

There's more than one way to skin any given cat, and there is good reason for this particular cat to be nervous right now even if leaf shutters in small format never make the scene.