Why? Unless you have money burning a hole in your pocket (some UW photographers do seem to suffer from this problem
) then save your money.
My rule of thumb is the new camera had better be about 10x better than the old one for me to switch. Consider the camera cost (which can be high for a newer model) and then the huge investment that is the housing.
Also, sometimes getting the new camera is the nudge you need to re-evaluate lighting options, so you can end up dropping a huge amount on new strobes, video lights, etc.
That's why my rule of thumb. I have a G16 in Ikelite housing and it's a great camera.
Also - consider your photography needs. Unless you are diving 200ft visibility with awesome colorful life, then the megapixels of every point an shoot camera now available is more than adequate for UW photography. Unless the GX7 has some feature you can't live without, save your money for now.
Now: I don't know the GX7 at all, but to me some features worth upgrading in the past have been: HD (i.e. 1080p) video; better low light capability, especially focussing; continuous auto-focus on video; 4K (proper, not pretend) video capability, etc.
I bought the G16 because of it's video compared to my Canon A570 IS. Just so much better (and 1080p!). That was enough reason at the time as I was taking a lot of camera video. Now I have a Canon 7D for photos and use a go-pro 4K clone for video. It's not as good for close-up video, but a ton easier to use overall.
In summary: carefully analyze why you want a new camera. Is it for a feature you don't have now, or gear lust, or just "because"?