I've read a lot of the PHP internals source code (I'm an author of phc), and this post leaves me a tiny bit optimistic, and a tiny bit disappointed.
I completely agree of the need to fork to make PHP a better language. The PHP internals community is the most awful OSS community I've ever been involved in, and getting shit done there just isn't going to work. So this is a good first step.
I also like the things he has taken away. PHP suffers from too many unnecessary options. I know that "unnecessary" is often subjective and in the eye of the beholder, but the OP seems to have a good eye for this. The things he removed are a blight on the codebase, so well done.
The optimizations are so-so. While I can see the benefits of the hardcoded constants, the other optimizations are hacks. And that has historically been the problem with PHP optimizations - they're all hacks. The engine needs rearchitecting to be fast, and all these hacks need to be removed, not more added.
Take for example that strlen is slow. The problem is that all function calls in PHP are slow. And if you looked at the function calling code, it's very obvious why. The correct solution is to make _all_ function calls fast, presumably by using some kind of inline cache, or just refactoring a ton of that crap out.
(Actually, someone introduced a patch to PHP-internals about two years ago to cache function calls somehow. I don't remember the exact details, but it was similar to the concept of an inline cache, perhaps storing a function cache struct in some bytecode or something. As I recall, it was denegrated as not being a full PIC. Sigh).
Finally, I really don't like the added functions. No problem with the functions themselves, just that adding functions to core PHP is not useful to anyone but the author. What if they clash with a user's function names? Why couldn't they just be implemented in user space? Etc. This is very much going on the wrong direction.
In the future, I'd like to see an effort like this go wild and make backwards incompatible changes like making the needle/haystack parameters consistent, but that's optimistic. (If they were to do it, phpcompiler.org could well be used to provide a 2to3-like too for doing the user-code porting automatically).
So overall, some good and some bad. If the OP focussed on making optimizations which improved the code base, removing more crap, and avoided adding "new" things, this would be really nice.