I know they originally have/had Ivy Bridge chips in those tablet-pc's but since Haswell has come out it is the PERFECT opportunity to swap those Ivy's for Haswell's.
Why?
The Surface Pro has poor battery life. (4 hours if memory serves) and Haswell has supposedly lowered power consumption.
Honestly it would be a great move to put in Haswell chips instead of Ivy's.
However I also heard Haswell has more heat problems as well so I don't know how that will work out.