Leaf shutters have a very high flash sync speed and that was great, but now with such great HSS available the need is really not there, in my mind. And as a plus, with the interchangeable cameras, we can sync to 1/4000(8000) with our aperture wide open and no ND filter needed. I like that the X100 series has a built in 3 stop ND and how quiet the leaf shutter is. But to shoot wide open with a clean exposure your speed is limited unless you use the ND. I think the x100 series is an interesting camera I still don't own one but I do love the idea behind it.
Yea, I already do HSS with my other system. It works. But it's clunky and requires extra stuff, or modern/expensive stuff to do it (especially HSS & ETTL together). Being able to sync without the light specifically having HSS as an option (because not all HSS is the same, some are long burn some are pulse, etc, and all of them you lose power doing it compared to standard output) means you actually have more output from your lights than you normally could have (not losing power by being in HSS, nearly gaining a stop of light back). So while yea we can buy interfaces that allow HSS to work, being able to have HSS without the light being capable of today's HSS is more interesting to me because you get the full power of your light that wasn't meant for HSS in the first place and you're not re-buying lights (which often cost more than these camera bodies!). Having a built in ND filter is great, there are other cameras with that too, I wish it was more common as an option, it's in the high end video stuff. Not having to fool with it as an extra thing to carry, one more thing to have multi-coatings to resist negative effects, one less thing to get dirty, one less thing to adapt, etc. Having a leaf shutter & a built in ND filter into the body is quite awesome for a camera body because again it allows you to use any lights in a very different way (suddenly your non-HSS lights are HSS capable). Sure, you can get all that stuff and not need this. But again, not everyone wants to replace all their lights from a few years ago, especially costly strobes. It's just a nice option to have. I definitely don't care to constantly fool with my HSS transceivers both on my lights, my camera, etc, more batteries to take, keep charged, etc, and of course the expense of buying all that in addition to the body & lights to begin with. My bullcrap $50 indoor studio strobes (Flashpoints) now sync at high speed with optical slave without buying a single thing to make it work (not that I need this, just the point of what I'm saying, my good outdoor 600Ws portable strobes and my indoor strobes, my manual speedlite fleet, etc, all do high speed sync without losing power and without the modality of pulse/longburn at 1/4000s if I want, without buying any additional things, really cool how it effects my whole system, and not just a specific bit of it).
Would love to have this feature set on an interchangeable lens body. But I realize that's not happening with these smaller format bodies, and seems to be reserved for the medium format and larger options. Not going there for cost. The X100 series gives you a taste of the simplicity of a larger format system with respect to lights and syncing, etc, in a way. Luckily I will never talk myself into a medium format system though. No way to afford that. I'd rather have a new boat! Lol. That and I'm sure I'd eventually get pissed at the slow AF of all the medium format digitals that are not $80K+. I live in a $500 camera world anyways! And then again, a newer medium format sensor, I'd be less likely to feel the need for lights probably in the first place, as that would be the point for me, to gain that zany dynamic range for outdoor shooting.