Nope, no barrier :)
From the Olypmus E-P2 to the E-M5 I saw a big leap in high ISO performance, about equivalent to what I saw between Nikon D200 and D300. The E-M1 has no low-pass filter and therefore slightly different noise characteristics that could be seen as "more noise" when pixel peeping, but otherwise it is more or less the same as the E-M5.
Look at it this way: APS-C and FF will always have either bigger pixels at the same resolution, or more pixels of the same size. As nobody has access to exclusive technology, you can always expect bigger sensors to perform slightly better at high ISO. There is no reason to expect MFT to ever "catch up".
On the other hand, there is something that YOU use your camera for, and that is taking YOUR images. My images are mostly made of static subjects, I am no action shooter. Sometimes I like to play with shallow DOF (and I can with MFT), but more often I like the whole scene in focus. On MFT, f5.6 is fine for deep focus, at least if I don't focus too close. Think of architecture, landscape or street photography. On FF you'd have to stop down to f11 for the same DOF. These are two stops. Now compare this with a FF camera like, for instance, the Nikon D610.
On the E-M1, thanks to five-axis sensor stabilization, I can hold my 25/1.8 at 1/10s all the time, and that without a proper steady stance. In fact I have just tried with the 12-40/2.8 at 25mm: I can repeatedly take images of critical sharpness at 1/10s, and that while holding the camera in one hand and away from my body. Taking a proper stance I can always hold 1/6s.
You can't do that with an unstabilized 50mm prime lens on the unstabilized D610. The rule would be one over focal length, but let's assume you have steady hands and can reliably hold 1/30s. These are at least two more stops, and in sum that translates to the difference between ISO 200 and ISO 3200.
Is the D610 at ISO 3200 as clean as the E-M1 at ISO 200? It's not. It has slightly more resolution and with a little bit of noise reduction and scaling down to the same size you may come near. Dynamic range will suffer though.
Thus, for my applications the Nikon D610 has zero advantage in image quality. In all other respects it is worse. It's heavier, bigger, and the more lenses you add, the worse is the difference in size and weight.