Another way to look at it is that unlike e.g. each, the docs for map and grep do not say anything about it not returning values in order (not to mention that the examples assume it).
in reply to Re^2: Order in which grep/map receive elements
in thread Order in which grep/map receive elements
Also, looking at the pitfalls of emulating fork on Windows and possible "thread safe" concerns, I would hope that any parallelization would be introduced in some optional way, such as a new function (e.g. pgrep), or using pragmas to turn it on or off. Or worst case, even if none of that occurred, I would be shocked if there was not a way to compile perl without a parallelized grep.