User blog comment:Lukeatlook/Pyro's Item Overhaul 5 - Supports and the CDR Overload/@comment-1748472-20140719142130/@comment-3466579-20140720101421

That's quite a good idea in my opinion. It's really easy to get to the 40% cdr cap and sometimes you really need a certain item for all of its stats but cdr (since you're already capped). Every item with cdr should have one of their other stats (e.g. health, mana, mana regeneration, ap, etc.) to be increased (by a certain amount, the % amount idea is not bad) the moment you buy that particular item giving you more than 40% cdr.

The problem is not in the cap itself (just look at the cap on attack speed) but in the ease to reach that cap. With 10% cdr from masteries and a 20% cdr item (e.g. Talisman of Ascension) you will reach the cap with a mid tier item like Fiendish Code or Kindlegem...