> Beginning with the type inference (ie using "auto" to declare vars).

GCC (and possibly other compilers) had typeof in the '90s well before D was first released. Macros in the form:

   #define    TYPEOF(name, expr) typeof(expr) name = expr

I'm sure that C++ borrowed concepts from D, but type deduction (not inference BTW) is not one of them.

Extensions are not part of the language, which means that programmers tend to avoid using them.