Every new mage item gives cdr and mana regen. EVEN zhonyas and abyssal will give cdr. Those are pretty popular items for him and he doesnt need cdr at all. Rumble is fcked up allready and he will be dead after mage update. He has one of the greatest ults And kits in a whole game. Please dont destroy such great champion. #makerumblegreatagain 
Sry for bad english but hope u guys underatood!
It's not like cdr it's bad for him, he just doesn't need it other than on his ult, but he can still use the other stats and passives the items provide. That said: hextech rocket belt seems like it'll be op on him.
Abyssal got more MR, more MR reduction, and CDR for a loss of like 20 AP. Rumble will be fine, Kat will be fine. CDR is unnecessary on both of them, but unlike mana, it's not a completely useless stat on either of them.
in the jungle!
Rumble is not one of the best designs. He's not even a good one.
Keep him in the gutter until he can exist without ruining top lane
I know I'm a little late to respond to this etc... but I did a post covering the changes etc on Reddit which may shed some light: This links to the currently active 6.8 changes This links to the planned 6.9 changes
And for those of you wondering what kind of validity I may have as a random commentator, I've been a Rumble main since S3 (close to 300k mastery points) with a pretty successful guide that has received decent feedback so far.
I hope this helps in some way - Fingers crossed for the return of our and his beloved TRISTY to win rates over 42% !!
