"you are saying that the Republicans don't require any fundamental shifts in their platform on social issues to remain relevant?"
I personally would be happy if the Republican platform was completely stripped of all mention of social issues, but this is not something that would benefit the Republican Party. Like it or not, there's no disputing that religious conservatives constitute a very large and important bloc within the Republican Party. They have large numbers, turn out to vote reliably, make campaign contributions, and - most importantly - they've shown like no other large political demographics that they *will* bolt if they're not happy with the candidate the party power-brokers are handing them.
In contrast, how many people would be won over to vote Republican if 'moderated itself on social issues' as people are claiming they must do? Where are the millions of gay voters who'd love to vote Republican, but can't because the Republican Party isn't gay-friendly? Where are the millions of hispanic voters who vote Republican today because they fondly remember the Reagan amnesty of the 1980's, or would vote Republican if there was a new amnesty? Where are the feminists who will leap to support a Republican candidate if only the GOP would come out in favor of abortions?
I daresay that the arithmetic is not in favor of change when you put these groups in the scales against the tens of millions of religious conservative voters and activists in the Republican Party. For many of them, abortion in particular is an issue they will brook no compromise over - any softness on this issue alone would cause literally millions of voters to simply not show up to vote. I do not see millions and more flocking to the Republican standards to take their places out of appreciation for change on this plank.
"it's exactly the mistake they made in 2012, telling themselves over and over that everything is just fine the way it is."
No, the mistakes they made in 2012 were nominating a terrible candidate (a Wall Street crook in the wake of a major economic catastrophe caused by Wall Street crooks? were they serious?) who ran a terrible campaign, surrounded himself with disgraced Bush cronies, and alienated the one primary challenger who had a proven ability to attract large numbers of new voters to the party (Ron Paul) and his supporters.