The fact that this _type constructor_ finds its way into _identifiers_ create some concern: https://github.com/dlang/phobos/blob/656798f2b385437c239246b59e0433148190938c/std/experimental/allocator/package.d#L642
Well, ISharedAllocator is indeed overboard, but at least `allocateShared` would've been a very useful identifier indeed.
