I think London 2015 is likely to be a real shoot out featuring pretty much all the major players [Kimetto, Kipsang, G Mutai, E Mutai, K Bekele, Kipchoge, Kebede, etc] gunning for the "softest" of the major CRs - it's "only" 2:04:29. I'm pretty sure all of these guys see winning London + setting the CR there as a bigger deal than winning worlds [+ it would certainly be possible to try doing both, although AK may try to prevent the top Kenyans from attempting it.]