Well, to offer an alternative point of view, my disappointment with the GM5 is that it's too big. I like the fact that the GM1 is tiny, and can easily slip into my pocket with a small lens like the 12-32mm attached. Anything that makes it larger defeats its purpose, to me. I understand that there are compromises when making a tiny camera, but I'm more than willing to accept them in order to get a super-capable tiny camera.
If things like grip, flash, and comfort with large lenses mattered a lot to me I wouldn't get the GM1. There are many other options in m43.