I believe it all depends on what you're looking for. Because on-camera flash kinda sucks, whatever the brand. I was with Canon before and I envied Nikon (just because they're a tad bit better than Canon on that side). For the sole purpose that, sometimes, you don't have a choice to slam the flash on the camera, I got myself the EF-42. With a Sto-Fen Omni-Bounce or a Gary Fong Lightsphere, it does the job pretty well. And even better than Canon, in my opinion.
I'm not sure I really yunderstand what you mean by "...there's no lens or camera or sensor that will truly make me commit to the Fuji X system." The lenses are f-ing great, the sensor is amazing - even the 1st generation in the X-Pro1 (wich I love more than my X-T1, btw), and the image quality is there. I even rarely shoot RAW anymore because most of the time, the JPGs coming out of the camera are better than the ones I do myself with the RAWs.
Did you spend a bit of time with a Fuji? For a least a couple of hundreds of images? If not, find a way to get one, and spend a reasonnable amount of time with it.
Oh! And by the way, you know you can order stuff online? Like the Nissin i40 you were talking about... Just order it online.