[»+^=«] reminds me of a P5 regex that has a comment saying "This is black magic. Don't touch!". --That's-- my complaint.
Indeed. There's a time and a place for that sort of black magic, and it's usually about once per 5,000 lines of code, and so deep and well wrapped in comments and unit tests that nobody should have to touch it. Ever.
If using something like [>>+^=<<] (and I'll bet a LOT of people are going to have to type it the long way) is going to involve 5-6 lines of comments just to explain what is going on, what's the point?
I look at...
>>but the basic operator there is just ^, with a + modifier to indicate >>numeric XOR, = to indicate an assignment operator, »« to indicate >>explicit parallelism, and now  to indicate reduction
...and I just mind-wipe... so it's doing WHAT exactly? I've read it 5 times and I still have no idea. And reduction? I write 25,000+ lines of Perl a year, and if you are talking about something like List::Util::reduce, I think I've used it maybe twice?
That sort of "pill" is the sort of think I'd assumed I'd start seeing once I wrote.
Which, by the way I'm completely positive about. Loading in special grammars for particular classes of programmers is just an amazing idea.
But really, in what circumstances could someone possibly need reduction so badly it needs to be in the core?