I don't think this is a good idea. He was a poor candidate the last time around, and a very weak field was a big reason why he won the nomination.
Romney Tells Donors He s Mulling a Presidential Bid - Bloomberg Politics
But there
is historical precedence:
1940 - Thomas E. Dewey (R) runs, loses at the convention. The guy who beat Dewey at the convention (Wendell Willkie) loses the GE to FDR (D)
2008 - Willard Romney (R) runs, loses at the convention. The guy who beat Romney at the convention (John McCain) loses the GE to Obama (D)
1944 - Thomas E. Dewey (R) runs, wins the nomination, loses the GE to FDR (D)
2012 - Willard Romney (R) runs, wins the nomination, loses the GE to Obama (D)
1948 - Thomas E. Dewey runs a THIRD time in a row, wins the nomination a SECOND time in a row, loses the GE to Truman (D)
2016 - ???
Run, Mitt, run! I see a statistical pattern forming!