Most of that code is for optimization or error messages. I think you could strip it down to:

    auto for_each = [](R&& r, Fun fun) {
      return r | view::transform(fun) | view::join;
    };

I also removed inline and constexpr because he didn't need them in his example.

I don't disagree that it's ugly, but it's not as bad as it looks when you go through the standard library. Those are functions that have been written, optimized and generalized to handle all sorts of cases. Your needs are almost certainly more specific, and you will undoubtedly write functions that are much simpler.

That being said, I kind of agree. I would have preferred your list of features to getting Concepts. I find SIMD to be a particular sore spot.