Greetings,

Question: "Are there any issues with this difference in elevation?"
Answer: Yes, your wife might trip and go down on another man. The
transition piece might make it less likely, but the uneven floor will
always cause a slightly higher tripping risk than a level floor.
Taking the risk is your choice.

Question: "Are there any wood flooring systems that stand out above the
rest?"
Answer: Assuming you DO NOT have a moisture problem I would go with
whatever solid hardwood looks most pleasing and costs the least. The
thicker the better as you will be able to sand it more times.

Special Note: You could tile your kitchen at the same time and get rid
of the elevation problem.

Hope this helps,
William