I like base 12 a lot, but Reverse Polish Notation is a mess when you get up to working with polynomials.

With polynomials, you're moving around terms on either side of an equation, and you combine positive terms and negative terms. In essence, there's no such thing as subtraction. (Similarly, division is a lie; you're actually just working with numerators and denominators.)

Reverse Polish Notation makes that a mess since it separates the sign from its term.

Also, RPN draws a distinction between negative values and subtraction, but conceptually there is no subtraction with polynomials, it's all just negative terms. (Or negating a polynomial to get its additive inverse.)

But, yeah. It's a shame we don't use base 12 more.