I sometimes ponder what I'd fix, given the chance, about PHP: * Make the "stdout == response body" an explicit option, and make a rendering engine the default instead. Just sending all output is a senseless DEFAULT. * Remove all the array_x functions and turn arrays into a class instead, and change the parameter order to be consistent across all the functions. A similar action could be done across many other classes…
Unfortunately, the biggest hurdle at this point is reputation. No full or dot release will change that.