I am also super fascinated by Mitt Romney's backdoor run for the nomination here.
I didn't understand his big speech at all until the Vox article on this:
http://www.vox.com/2016/3/3/11155110/mitt-romney-donald-trump-speech
If they actually go to a contested convention, the GOP establishment needs to find a candidate that can unite the Cruz, Rubio, Kasich, Jeb, etc. delegates.
That candidate is unlikely to be Cruz, Rubio, or Kasich, because if they wanted to unite behind one of them, they could just do it now.
So they need another candidate. One the GOP can easily support, one who can be viewed as a strong contender against Hillary, but one who for whatever reason chose not to run this year. Mitt Romney is a great choice for that role.
Of course, I don't think Romney can win (although he is actually probably one of the strongest candidates the GOP could run). Once they blow up Trump he'll probably follow through on his third-party threat, if for no other reason than to prove his threats should be respected. But he would be a good "elder statesman" for the non-racist, business-focused side of the party.