Generally, PPT's have stated that the line should skip to the SoS. The real question will be on President Kerry.
What?
The PPT has the constitutional authority and the constitutional responsibility to become President in the event the President, the VP, and the House Speaker become incapable to serve.
Not the SOS.
The constitution was amended to change the line of succession to PPT and Speaker and later Speaker was put ahead of PPT, and cabinet follows, due to the fact the Speaker and PPT are elected officials, whereas the cabinet members are appointed officials.
I have no doubt whatsoever that, should it become necessary, that the Speaker, and then the PPT, would carry out their constitutional responsibilities to serve as President.
I completely disagree with your statement.