Not a switch, per se, but I have recently acquired an X-Pro 1 and three lenses - The XF 35mm f1.4, XF 27mm f2.8, and the XC 16-50mm 3.5-5.6. I have been interested in the Fuji almost exclusively for the optical hybrid viewfinder since it came out, about the same time as my E-M5. I've been very happy with my E-M5, which was clearly a better choice for me at the time, and I would not, at this point, be willing to give up the in body stabilization (so no Panasonic m43 for me either), but I do find an EVF, even a very good one, sometimes gets in the way of things. I experience the video VF increasingly as a barrier between me and the world I'm trying to see and respond to. Thus the X-Pro, three years old and less responsive, and not the XT1, which sound like a phenomenal camera.
I've owned and enjoyed using the X-100, the X-10, and the X-20, the last of which I still own. I'm not interested in the X-30 precisely because of the EVF, no matter what other advantages it brings to the table. The X-Pro fits right in with how I have approached the Fuji cameras from the start.
I'm not denying Fuji's stellar optics, the advantage, slight though I find it, of a larger sensor, or the special beauties of the X-Trans version of APS-C. But the IQ from my E-M5 with the 25mm fl.8 or the 45mm 1.8 satisfies me completely. A bit more grain at higher iso never has bothered me, since I shoot raw, and color noise, the only kind that does bother me, can be easily dealt with in any competent raw converter. The two lenses mentioned above do Olympus proud, and I've found the rendering of Olympus' optics pleasing for over 30 years.
So, do I have a preference? Depends. Depends on what I want to do. The immediacy of viewing through an optical finder forges an intimate connection with the world that is hard to achieve with an EVF, at least for me. The information in the Fuji overlay is nice to have, but I happily use the optical accessory to the Leica X1 and find the experience -- well -- wonderful. The important thing is the un-preprocessed view. The rangefinder like frame in the middle of the finder is even better. I've rarely been able to see an entire viewfinder with my glasses on, without moving my eye around, and I prefer not to go through the hassle of taking glasses on and off. Putting on my glasses is the first thing I do in the morning, and taking them off is the last thing I do before turning the light out at night, and it's been that way since my middle teens. Stumbling around without them, like Mr. McGoo, while I use a diopter correction to shoot is not, for me, a realistic option. So, the frame lines experience is very much to my liking, even if the advantage can disappear with wider lenses. The 24mm (16mm) field of view is not one I use a lot, though it's nice to have a zoom around to give me the option.
My ideal camera would have the speed and versatility of the E-M5, along with, importantly, its in-body stabilization, and the optical hybrid viewfinder of the X-Pro. The larger sensor would be nice but not essential, and I could live with either an X-trans or Bayer. Using a 300mm legacy lens, hand held without in-body stabilization, is a chore, and until I can replace my birding lens with a digital OIS version for the Fuji, opting out of the Olympus system is unthinkable to me.