The DOT 5 bottles say "not for use with ABS" on the label. Many have speculated on the reason. Silicone is more compressible than new glycol, though after a year or so the glycol can absorb enough moisture to make that not true. Compressibility could affect the pulse rate of the ABS unit. My guess is that car companies don't spend the money to qualify their ABS with silicone fluid. I doubt there is a seal compatibility problem since the DOT regulates that all brake fluids work in all systems, plus there were some 1950's British cars that required silicone since glycol attacked their seals. One guy said he was going to try DOT 5 in one of his ABS cars. Worst case is probably that the ABS would pulse a bit differently.

I thought ABS used much more volume of fluid (silicone is expensive), but doesn't seem true when I bleed them. It would be harder to get all the glycol out of an ABS unit and many newer cars have dual brake tubes to the rears (X-pattern MC plumbing), so more work to fully flush. In my case, I might sell my older 1996 minivan in a few years (currently use as a truck to haul stuff), so no sense changing it.