nice idea. I will also toss here the suggestion I made on another thread.

How about a "scan" skill, juste like there is in many FF games? No agro icon nor lvl indicated (as it seems the dev are talking about currently), but once you use the skill on the mob, you have the relevent information (+elemental strength, hp/mp, etc). after a while the info fades. so no intrusive ugly icon.
All the info collected could then be placed in the codex and available to you anytime.