Depending on who the next Conservative leader is I could see them backing Labour on certain policies. Trident renewal is a definite. If the SNP try to hold Labour hostage on the budget I could see the Tories coming to the rescue, at a price.
But in short a Grand Coalition is unlikely. There are deep differences in ideology and identity between Labour and the Tories, regardless of all this posturing about them being the same. It would also be electoral suicide. A lot of people vote Labour or Conservative due to their hatred of the other party, and that voter base would evaporate if there was a 'Grand Coalition'.