[zvrba]

Couldn't you expose machine-dependent stuff in a subclass?

SSE has a bunch of other useful instructions like PMOVMSKB (useful for fetching the result of vectorized comparisons, yay!), then there are string instructions (sometimes also useful outside of string processing), etc.

New versions (AVX-512) will also have mask registers for masked operations.

[chinpokomon]

It sounds like they're trying to maintain platform independence while still abstracting platform specific low-level operations. If you utilize machine specific code in subclasses, how do you generate MSIL that remains independent?

If you really needed something like that, could you not use C++/CLI and expose those operations in your own unmanaged library? You will of course lose portability, but that seems like a possible work around.