And my response is the same as always: the ease-of-use argument is a red herring. End user expectations are often misguided, and doing something wrong, on purpose, to fulfill those expectations is bad design and simply perpetuates misguided expectations. Input via pp-lib sequence is insignificantly different in terms of number of typed characters. The difference is typically two parentheses--one at the beginning and one at the end (", " is the same number of characters as ")(").
As a pp-lib user, I find it much more cumbersome to write "MY_MACRO((a)(b)(c))" than "MY_MACRO(a, b, c)" - primarily because the latter requires a lot less keyboard acrobatics - and I have written my own equivalent of VARIADIC_TO_SEQ to allow me to write the latter. Nate.