So, about half the supports can use the stats on Kage's Lucky Pick, but for the other half it is useless. The gold pressure is a *little* less intense, but the loss of a second GP10 is sorely felt on these champs. Especially with all the new support-focused items that are really hard to buy without that second income stream.
It's probably the most rough on Leona. She can't make any use of Kage's, and can't use the pickpocket mastery at all. Throw her and maybe Alistar a bone?
And finally... Pickpocket. Assuming you can get an attack roughly every 6 seconds it is worth (for ranged) 5GP10, for melee it is worth roughly 9GP10
Leona is relatively effective at using Pickpocket compared to other melee supports. She requires aggressive play and consistently attempts to engage the enemy. As long as she gets one attack on an enemy in every ten seconds she's getting a HoG out of pickpocket (hint , you have an AA reset stun combo)
Yes certain supports cannot use kage effectively. However those supports are aggressive tanky supports with personal steroids which already amplify their value of gold more greatly than the steroids of other supports. That's also why Kage is only 4GP10 (and why pickpocket is worth 2GP10 more for melee than ranged)