The K-3 is a beast. It is very capable at high ISO. A PF member even argued that it is better at high-ISO than the K-5iis (hence the K-30) when you downsize your shits to 16 Mp.
You asked for improvements. Yes AF can be improved. But we also want to see some continuity, including:
-Body ergonomy and build - I love the body ergonomy and build quality of the K-7/
K-5/
K-5ii/K-3.
-WR - I value highly WR because i shoot mostly outdoor. Pentax is the only manufacturer who provides a choice of sub-$1200 dSLRs with WR.
-IQ - No need to say more... as there have been so many thread on the topic but Pentax has done very well with the K-5 sensor family (K-5, K-01, K-30, K-50, K-500, K-5ii, K-5iis).
-Backward lens compatibility - This is a key asset for all Pentax users: we can re-use our lenses immediately; no need to buy new-ones. I believe that this argument has not been marketed enough.
-Small body - I value a small body and Pentax has an excellent experience with smaller dSLR bodies.
I would love to see some continuity and enhancements in the K-3ii, while retaining what bring me to Pentax.
Hope that my 5 cents will be of interest.