Increase Banner of Command's CDR to 20% up from 10%

This will blow your mind man get ready for it.

..... No really strap your self in... Okay here goes:

15% Cool Down Reduction

whoooah, I know right. Let it set in, you'll see the world in a whole new way.

Banner of Command is one of the few items in the game that can actually provide your team with a win condition lol. You can literally get 2 dragons, baron and Banner of Command and have the cannon minion carry you into their base. Also, it is primarily a support item. A lot of supports go over the 40% cap with Banner's CDR at 10%, so raising it seems silly. Also it provides everything an AP support wants in CDR, AP, and Aegis passive. It also is still viable on Heimerdinger as he gets a HUUGE boost in pushing power from its active when the tower takes longer to kill the siege minion and not his turrets. Plus he gains a lot more from 75% health regen since his base health regen is by far the highest in-game. Plus his passive+aegis passive actually provides significant healing to teammates. Plus the MR helps him chill inside his turret range longer.

There's not really a big reason to make the item a standard build purchase because then it would be too strong in the niche situations that it is already incredibly useful.