I think it's far more likely that the U.S. will stop using ounces, pounds, feet, miles, pints, gallons and what-not, and move over to the much more sensible metric system. Unfortunately, I don't see that happening any time soon, so tau will continue to be just an afterthought. You don't toss out widely accepted conventions without a compelling reason, and the case for the metric system is surely much more compelling than the case for tau.
Anyway, there are any number of formulas that use pi. Sure, you could substitute in (tau/2) in it's place, but then you'll be dealing with all kinds of annoying fractions. Yeah, tau*r is simpler than 2*pi*r, but pi*r^2 is simpler than (1/2)*tau*r^2.
Hope that helps!