I'm sort of a generation behind still loving my Oly 5 D-II...just 16 MP. In high-res mode (sensor-shift, 64 MP raw files), very good 30x40 prints and larger quite easily, at least as good as my Nikon D800 and its 36 MP, maybe better. However, the largest image on my wall is from a GX-7 16 MP and is 30x40. From less than 2-3 feet away, it's reasonable... from across the room, it's got impact.
With good craft starting with the capture with the better lenses and tripod through good post processing, these little cameras can create quite large prints rivaling the images from larger formats with every bit of similar quality. I would not hesitate running the best files large! However, YRMV.
A lot of my current work requires shooting at nose-bleed speeds, ranging from a low of 1600-3200 and many times pegged to the limit in "hail Mary" lighting (candles in a dark church) and hand-held. I could probably get a little bit better files using a current full-frame and premium lenses, but size, weight and more importantly silence/stealth is key to my work and allows me continued access. Seldom am I afraid to print these as 11x14 or even larger images. In my case, the moment and gesture is more important than the absolute pixel quality. These are neither fine-art nor landscape so totally appropriate to the final image.