Ben Hutchings began extrapolating data of stable kernel releases and around the time of the Debian Jessie freeze will likely be the Linux 3.17 release, but that might be too close for comfort. However, at the same time, the earlier the Jessie kernel is frozen the more hardware enablement back-porting and other fixes that will need to queue up for this next major Debian GNU/Linux release.
Ben proposes that the Linux 3.16 kernel is likely the "best fit" and that the 3.15 and 3.17 kernels likely won't have the kernel real-time (PREEMPT_RT) patch-set but should have for 3.16. There's also hope that the Linux 3.16 kernel will be a long-term stable branch.
Based upon this information, it looks like Linux 3.16 will likely end up as the default kernel for Debian 8.0 "Jessie", but things may still change. The discussion can be found on debian-kernel.