If it was only one shitty ancient system it would be one thing. For the company I work for it's about 10 big interconnected mainframe systems with hundreds of non-mainframe systems cobbled together around them. They've been in place since the 80s, but you can trace their business logic back to the 50s and 60s. They start at cataloging all our parts and get into purchasing components from suppliers, describing the products we assemble, managing the supply chains for our factories, order management from our customers, etc.
Replacing it all will be massive chore, but it's becoming more and more clear that we need to. At the end of the day, capturing and understanding data in them takes so much skill that we have entire departments dedicated to being an interface between the actual users and the mainframe. The business rules might have worked before the products we build contained electronic controls, but everything is starting to implode now that "parts" also includes software. This has resulted in manual workaround on top of manual workaround.
There aren't many DSLR like fixed lens cameras out on the market today as that segment has basically evaporated.
The remaining players are:
What are you looking for that the G1X mkIII doesn't offer? Buying a used copy might be the way to go, especially since it sounds like what you're looking for.
As far as currently in production options, in addition to the three above, you could also look at mirrorless. Both their bodies and lenses are more compact than their DSLR counterparts. As far as sensor size goes, Micro Four Thirds (micro four thirds) can offer the most compact glass, followed by APS-C and then FF. That said a compact FF body, with a slower (read: smaller) lens will generally be close in size to a MFT camera with a fast lens. For outdoor and sunny, there will be no image quality tradeoff and when it gets dark the FF camera with a slower lens and a MFT sensor with a faster lens will be more or less on par thanks to the FF sensor's two stop improvement in low light. For example (scroll down if you don't see the two cameras and lenses). This does start to fall apart at longer focal lengths though - there's no substitute for the crop factor advantage beyond say 100mm of FF EQ focal length.
So... What are you looking for?