Just wondering here, Xyph, whether you even know about the idea to remove the CDR cap and implement diminishing returns on CDR such that its effectiveness scales linearly. The new system would work something like this:

Introduce a new stat that is similar to armor, but instead of reducing damage you take, reduces the cooldowns on your spells. In the tooltip, it can say that the stat increases the amount of spells you cast by the percentage of the value of the stat. It can literally function with the same exact formula as armor reduction and work linearly in terms of DPS increase from spell casting. For example, having 100 of the new CDR stat would increase your spellcasts by 100%, which is effectively 50% CDR, which is what you get if you plug 100 into the armor reduction formula.

I say this because you mentioned earlier that you had to be careful in putting CDR on items because of the CDR cap. In this new system, CDR would be able to be more widespread on items, and then having weird percentages on runes and masteries would not lead to wasted CDR. Currently, CDR runes are somewhat useless because the way CDR scales, any amount of CDR you have makes any CDR you get in the future more effective. I know you understand the math behind this because I saw you post about what would happen if percentage armor penetration/reduction stacked additively rather than multiplicatively, and the way you described it is EXACTLY what happens with CDR. It may be too late, but while you are doing a massive overhaul of the item system, why not implement this rework to the CDR system such that it is more standardized and balancable? Of course the values of CDR given on every item would have to be changed, but it would definitely be possible to do and keep the game balanced.