I think if you make it fit the Bosch, DeWalt, Makita, Triton, Milwaukee, Ryobi, and Porter Cable routers you will cover most of the newer and better US brands. I have no experience with the European or Far East Brands.
I mostly use DeWalt 618B3 routers with all three bases. I have three DW618's, but my new DWP611Pk is seeing a lot of use too, and I might be buying a second one of them soon. I have 12 routers total. Makita, Black & Decker, Milwaukee, and Porter Cable are also some of what I have.There's even a plunge base Dremel in the mix. Stick to what has been manufactured in the past 20 years and I think you will have enough holes in your tool to make it look like Swiss Cheese.
Central North Carolina