It would be the ultimate "team of rivals", with the last 3 people standing in the Presidential campaign part of the White House. Personally, I would prefer someone like Amory Lovins, but McCain might be a wise political strategy.
John McCain as Secretary of Energy? Let us first consider the major objections:
1. McCain's own position on energy and global warming. Among all the policies McCain pursued, in this area he most closely approached the position of Democrats. There were clear differences in scope and in emphasis, but it was never clear how deeply McCain believed in the mantra to which his base forced him to kowtow.
2. McCain's insistence on nuclear energy. It is unlikely that McCain would have been successful pushing this policy, on the scale he proposed, even if he had become President. Moreover, if the costs of storage are included (and, at some level, they must be), nuclear is cost-effective.
3. McCain's opposition to federal spending of any kind. This seems to be the one visceral principle McCain holds dear. The program will be $15 billion per year. Can McCain swallow that, and support it, regardless of what the elements of it might be?
4. McCain's insane temper. This would not be a policy problem at Energy as it might be at Defense or had he become President. Nonetheless, it might compromise his ability to steer complex legislation through the Congress.
5. McCain's lack of attention to detail. That would be a fatal flaw for McCain to be Homeland Security Secretary. It might be a problem for McCain defending particular policies before Congress as the energy plan is going to be among the more complex that Congress has to handle. There are, however, others in the Department who could cover for his inattention.
6. McCain's interest only in himself. McCain wrote very clearly that his personal ambition was to be President; indeed, he wrote that personal ambition was the only reason for his seeking the Presidency. Now, McCain's Presidential ambitions are over. In 2010, he faces a re-election campaign probably against a very popular Governor, Janet Napolitano, that will not be a cakewalk and he may lose.
McCain may now look at his self-interest differently. After the lame, and sometimes scurrilous, Presidential campaign he ran, John McCain is in need of some rehabilitation prior to his departure from national politics. Serving as Energy Secretary in an Administration that changes the energy game, and simultaneously addresses global warming, may be a decent legacy for him.
Are these flaws fatal either individually or taken together? It depends on McCain's willingness, or ability, to voice his objections internally, and then support the program the President endorses wholeheartedly whether or not he agrees with every element.
The most important hurdle McCain would have to leap is his abhorrence of federal spending. The energy program Barack proposed is $15 billion per year for 10 years. Whether McCain could swallow that, and support it vigorously, is unclear. That would have to be a major consideration for both the President-elect and McCain.
Would McCain be interested?
McCain might see being a part of a "Team of Rivals" as his ultimate service to the country.