Jumping onto the mirrorless interchangeable lens camera late, I missed out on the micro four-thirds line of cameras from Panasonic and Olympus, opting for models from Sony and Samsung because of their use of the larger APS-C sized sensors. MFT cameras, which are still going strong five years after they were announced, have an advantage over other MILCs with its vast selection of lenses from Panasonic, Olympus, and Sigma, as well as compatibility (using adapters) with many other lenses with different mounts.
And while I can't recommend switching to MFT if you're already invested in other MILC ecosystems, Panasonic's new Lumix GM1 may make a lot of sense as a secondary camera for DSLR owners. The rangefinder look-alike GM1, which has very similar specs to Panasonic's high-end GX7 (16MP sensor, 5fps burst, Wi-Fi), is notable because of its incredibly compact size. The photo below, from Imaging-Resource's preview, shows just how small the camera is in the hand. It's even smaller than Sony's awesome RX100 Mark II, which has a fixed lens and smaller sensor, and costs the same as the GM1. This isn't a potential NEX-killer, but it is an RX-destroyer if its photos are as good as on the GX7. There are a few trade-offs for the size: battery life, lack of EVF option or even a hot shoe, and no tilting LCD. But as a camera to throw into your jacket pocket and take on day trips (or ski trips!), the GM1 looks very enticing.
This is not, however, necessarily a camera for enthusiast video recording. The reduced body size lends itself to potential overheating (a problem we've encountered with other compact MILCs), so Panasonic limited video recording to 1080p at 60i instead of 60p. Also, the shutter on the GM1 is a new hybrid mechanical-electronic design, which while can achieve a speed of 1/16,000 sec, is still susceptible to the same rolling shutter artifacts as Panasonic's GH3 and GX7.
The Lumix GM1 will ship in November for $750, which includes a new 12-32mm f/3.5-5.6 OIS kit lens. A body-only kit will not be available, though the lens will be sold separately for existing MFT users for $350.