there is almost no possibility of a Surface Pro 3 coming out this year. They won't release an SP3 unless there is new hardware out there. A mild refresh of Haswell is not going to cut it because it won't improve battery life significantly, it won't significantly increase performance, and it won't decrease the size of the Surface Pro.
It will take something like the release of Broadwell in order for a new SP3 to come out. And Intel has delayed Broadwell until the end of the year at the earliest...
here's a good summary of the rumors. sure, it's conjecture. But it's well thought out (none of the following text came from me; I read it in another forum):
This is just my speculation:
But I think there's a lot of evidence that tells me the next generation Surfaces won't come out until 2015:
1) NVidia is developing the processors in the K1 Denver variant on their own, in addition to putting together the new SoC, and that is a lot of miracle-work to be doing by the time the S3 goes into production (according to Anandtech). Scheduling the S3 to come out in 2015 would be safer.
2) The availability of Broadwell is not yet a done deal, as defect density continues to plague Intel's new manufacturing process. Though, I have no reason to doubt their revised roadmap.
3) This is the biggest one; the original S/P were released along Windows 8, and the S/P 2 along 8.1. The 8.1's update 1 comes out next month, and Microsoft probably won't be releasing a whole new generation of Surface tablets then. Rather, an LTE version seems more likely, maybe a Mini, but neither Broadwell nor the K1 Denver is actually in production yet, so I don't think there's really much upgrading possible this early. If Microsoft wants to continue to release new Surfaces with a new update to Windows the same way Google releases Nexus devices with each upgrade of Android, then either there will be an Update 2 coming out in the fall, or the next gen of Surfaces will be pushed back to coincide with the release of Windows 9, slated to be released in April 2015. This puts the Surface release schedule back on track with the original release, although it does mean Microsoft will be without a brand new product going into the holiday season.
This is all just speculation built on rumors, what others have speculated, and a bit of my own reading of tea leaves. I really hope that all that production can be done by the fall, because I'm holding off to get a new device until then, and if a more tablet-esque SP3 is not coming out for 6 more months, I'll be unhappy. Looking at all the chips that are supposed to go in and hearing about the potential production delays, combined with the supposed release of Windows 9 in early 2015, however, makes me think Microsoft might be aiming for that.