Micro 4/3rds isn't really there just yet IMO (it may never) simply due to the fact it's difficult to get amazing IQ (read: IQ, not pictures) out of such a small sensor. However, an E-M5 with a 12-40 2.8 (which I HOPE to get for myself as a Christmas present) will be my ideal walk-around combo (and would be my travel setup). That combo is very sharp, has a great range, is 2.8, is weather-sealed and can do an effective 0.6x magnification. To get a significant step up in IQ and ISO performance, one really needs to go to FF (although the Sigma Merrill is amazing for IQ, but it is essentially useless in every other regard). However, the four thirds sensor is still great due to the large DOF at large apertures (so you can shoot in low lit environments but still have much larger room for error DOF/focus wise).
I just think it's too difficult to come up with a 'perfect' travel kit, as one is always compromising whether it be on size, weight, IQ, lens selection, ISO performance, cost etc. I definitely see the advantage of mirrorless for travel though.
I don't know if 4/3 is relevant at this point. Sony already released full frame in mirrorless in the same size. It's just a matter of time until all others jump on the bandwagon.
4/3 was barely adequate in terms of image quality when it was released and I don't see that small of a sensor offering something competitive a year or two from now.