I absolutely love this feature! It puts important info exactly in the spot where users need it. I hope to see this expanded in the future, to also apply to abilities, and display more information. For example to label what kind of damage bonus you get from a certain mod (Base Damage bonus (serration) vs. Enemy-Type bonus (Bane, Roar) vs. Final Damage bonus (Eclipse)). This is a major reason for the obscurity warframe's modding system, and this UI is perfectly suited to provide users with the necessary information that's currently wiki-exclusive. If info becomes too numerous, a toggle in the option "show advanced information" could be introduced (off by default) on which these math-related tooltips depend.
Imagine if you acquire a new mod like Master's edge and immediately knowing, ingame shown, how its damage bonus combines. Or seeing on Melee Animosity how the stacks exactly behave: Does acquiring a new stack refresh the other's duration? Do they drop off one-by-one when the timer ends, or all at once? Imagine having an ingame indication about how different Arcane Avenger's +45% Critical Chance behaves from True steel's bonus!
By utilizing the power of keywords (like Overguard, Decaying Stacks, and whatever else we can come up with) and this UI, Warframe can become _so much more_ transparent.
