There are options you can use already which will provide the same level of speed as direct port manipulation. constexpr functions would only be one more way of reproducing the desired effect.
The major problem holding back the implementation of these methods in the background of digitalRead/Write is the dramatic timing difference between calling digitalWrite with pin numbers as a compile time constant vs a dynamic run-time deduced pin number (for loop iteration).
EDIT: There is also no support for C++14 in GCC 4.8.1 (what the latest IDE uses), however you can enable C++11.
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