The GM1 and K-3ii are both excellent cameras with numerous features that add to their capabilities. Both have intervalometers for stop-action video or time-lapse imaging, sensor sizes are similar (4Thirds / APSc) so enlargements are of high quality, and each is pretty compact for its type. The Pentax adds weather seals, the larger sensor with more resolution, an optical viewfinder and really long battery life; the GM1 is essentially pocket size, can use its own or Pentax lenses, makes great videos with minimal fuss, and its touch-screen allows for precise AF and other rapid adjustments.
The 4Thirds sensor in the GM1 does very nice work; I tested it to iso20k and found it 'acceptable', meaning it looks rather like a phone capture except it's basically shooting in the dark. Studies like those at dXomark show the K-3ii wins for all sensor specs, but how often will I notice the dynamic range is narrower (especially when iA modes or shadow adjustments are enabled)?
The best news is really that the GM1 is so small that it can come along pretty much any time! However I must admit that for over a week the tiny Olympus 9mm fisheye had gone missing - that lens is so small and light that it was found in a day-pack pocket that I had already checked!