or maybe a properly focused flash, rather than powerful? 90mm sounds nice for closer portraits and such (on aps-c).
leaf shutters are not only related to large format. you can get a very cheap one to play with by getting a smena 4m (i think it was called, cmena spelled in russian), it is a sort of rangefinder, and dirt cheap. (it also happens to have been my first camera), it comes with a leaf shutter, in the (non-interchangeable) lens. it is simple and rugged, so you might find it fun to take it apart and see how it works
. in this case, the shutter is very close to the apertures blades, so to the optical center of the lens, i guess the main reason is precisely to avoid vignetting (you can get some light loss, but across the frame instead of local, as if stopping down a little, which leads to the discussion about shutter efficiency).
i am not sure how having a leaf shutter so far from the centre of the optical system would work, but i am afraid it would be practically the same thing as having a focal plane shutter (the same issues if you go over the "sync speed", only instead of sliced horizontally or vertically, you have it circular now, like a sort of very hard vignette), unfortunately, if i am not mistaking, the very point of the leaf shutter (also called "central" shutter as opposed to "focal" shutter) is to have it in the centre of the optical system, and that is also what gives it the virtually unlimited sync speed, not it's design in itself (if one would be silly enough to design a vertical travel shutter to work in the optical centre of the lens, you would get the same feature of unlimited sync speed, unfortunately, the opposite is also true: if you take the shutter away from the centre of the lens, you will get a focal shutter (or some freak hyper-focal shutter, or whatever), regardless of the way it uses to block the light, as long as it doesn't block all area at the same time, the sync speed will be limited by the mechanical speed of the shutter.
sorry. (i would be glad to be proven wrong
)