x86's terrible reputation is well deserved. x86-64 fixes a number of problems, but for most of x86's lifetime we've had to live with 8 registers and the lack of IP-relative addressing...
Let's not forget how awful x87 floating point was, either!
On the other hand, one of the things I like about x87 is that it's extremely dense because it's stack-based and RPN-ish. Here's 256 bytes of x87 awesomeness: http://www.pouet.net/prod.php?which=53816
But it looks like it's x86 plus SIMD. If so, then Intel probably has literally 1000's of man-years of validation suites for x86. If you remove some of the x86 instructions, how much of that test code do you break?
The Larrabee designers probably wanted to focus on the SIMD and on putting bunches of cores onto a single die. They didn't want to reimplement (or even fuss with) the x86 part. That's not what they were interested in.
Leaving x86 alone means the chip runs Windows, Linux, etc w/o any further effort. Or does it, like I said I don't know the architecture?
What do you gain by breaking that? It's probably a very small part of the silicon area anyway.
PIC can be emitted on older x86 machines without RIP-relative addressing, but the code is larger and slower. As an example, consider -m32 gcc output for the C program
int x;
int getx() {
return x;
}
getx:
movl x, %eax
ret
getx:
call __x86.get_pc_thunk.cx
addl $_GLOBAL_OFFSET_TABLE_, %ecx
movl x@GOT(%ecx), %eax
movl (%eax), %eax
ret
getx:
movl x(%rip), %eax
ret