That seems to be based upon a myth, that of the Conservatives remaining home. Those who did not show up for Romney, per the exit polls, were the mushy middle he was counting on by running away from the Conservatives. That said, I do not think another of the Progressive Republicans will be able to count on even that level of support.
Evertything I saw suggested that Romney got even more of the White Conservative vote that Bush did.
Face it, he was a dud of a candidate. He inspired no passion in even those who voted for him.
That is an excellent observation! The next GOP presidential nominee has to capture the mushy middle, while still advocating solid conservative values.
It can be done. Reagan showed us the way. But it won't be as easy as it was back in the Gipper's day. The welfare state is now larger, and the media is now more biased. So the GOP leadership has to be clever, very clever. Personally, I don't think they're up to the task.