Modular cameras have always been a big part of professional gear. Large and Medium format cameras were always highly modular as was the film based Canon F and Nikon F ranges.
Recently Sigma produced their very exciting fp modular camera. With the L mount from the L alliance you have access to the best Leica glass and more affordable glass from other manufactures. It is an interesting concept that deserves to succeed. This new model at 60 MP is quite a beast, and I can see if attracting landscape photographers and maybe a few product and studio cameras.