Describe the solution you'd like
When mousing over a skill in the inventory menu GUI skill list, a tooltip showing how much XP you have towards the next level.

Why is this feature needed
This would complete the inventory menu GUI in the sense that it could be used as a replacement for the Skill list HUD text, which would help with visibility at lower resolutions. I'd like to move away from the skill list HUD text and make use of the nice inventory GUI, but as it is now I don't think I can fully disable the HUD text without creating my own implementation for fetching XP and giving it to the player.

Describe alternatives you've considered
This would be harder, but displaying the amount of XP you have on the left side of the XP bar, and the total XP for the next level on the right side of the bar. This would look pretty, but be difficult to implement and may spoil the clean look of the new GUI.

I love this idea! A tooltip would be really nice and we could pack a lot of information into it if we needed to.