Including governors would be technically possible with a change of the law, but you then have the problem of how do you decide which governor gets first shot at being President.
I suppose using the order in which the states were admitted to the union is out of the question?
There are governors who are ineligible for the Presidency, namely the governator.
In which case it shouldn't be too much hassle to skip them, afterall cabinet members who're ineligible to become president are missed out of the line of succession.
I thought cabinet members have to be eligible for the Presidency to hold their position.
Bush's Secretary of Labor (and Mitch McConnell's wife),
Elaine Chao, born in Taiwan, ineligible to become President and full cabinet member, she was simply skipped from the line of succession.