>Is anyone aware of other arguments for not allowing normal arguments
>unpackable arguments in function calls?
CHU Zhaowei pointed to this git commit which suggests it's an implementation issue rather than a design decision: https://github.com/php/php-src/commit/d3b484df8268f7ab31c4ac39734d4b68ce2e6159
From Nikita's excellent commit message, it sounds like normal parameter passing is compiled in an optimised way that wouldn't be safe if run after a spread operator was expanded. Rather than adding a whole bunch of complexity, the edge case was just made into a documented limitation.