C99 would be nice, there is a lot of nice additions.
And we could remove a lot of the various ATTRIBUTE() style macros. And there are predefined types for integer-with-x-bits (fastest-with-or-at-least x bits etc). That removes another bunch of configure tests.
Also, there is of course a bunch of new alway-available functions.
And // is now valid. As is variable declarations in the code. And in for(>here<;;).
And the rounding functionality of % has been standardised. Unfortunately in the other way from the one pike uses. :)