With Pentax and Lumix now shaping up as thin but complete systems, the chance to improve on optics becomes complex. The best choices for good glass would be one that fit well into both systems rather than just one. So with that in mind, here goes!
The first step comes at around 30-40mm. Several nice Pentax options are available, but micro43 prefers to fill space just above 40mm and the Pentax 50/1.7 does just fine above that. My 14-42mm would be f/5.6 at the long end, and the 45-175 sits at f/4 - so a faster prime would be very nice to have! I see two options for sale right now: an older 35mm f/2 and a Limited 40/2.8. That latter lens would have modern coatings and be auto-everything on the K50, but the 35's aperture ring is handy on the G7. Since I've ordered an adapter that can adjust the aperture on K-mount lenses the DA40 is the better choice.. but really closer to the 50/1.7 than I would prefer. More consideration coming..
Another space in m43 is at the wider end. Many lenses are 14-xx and Lumix has a 14 prime - but what else? Samyang has stepped in with several fun choices, and the 7.5mm fisheye is a good call as is the 12mm f/2 for sky imaging. On the other hand, the 12-32mm zoom is tiny but well liked by owners and reviewers. It's another of those f/3.5-5.6 types which is a bummer.. but getting to 12mm (24mme) is a nice option to have. I see deals on that as well, so perhaps that will be wide enough - especially since the G7 has a panorama mode for times when wide-angle lenses just won't do. Good luck using that mode with a fisheye lens, it would be interesting to see how the camera handles such a request!
