All supports should be like Senna/Thresh.

As in they all need a way to power up outside of gold gain.

Supports like Senna and Thresh each have a mini game tied to them that makes them both far more engaging and rewarding to play as, especially when hitting the mid/late game.

Why not expand that for ALL supports?

Say Janna, every spell cast that hits an champion or epic monster kill a number of wind sprites spawn for her to collect? (A zone for her to move into to collect that spawns from her spells.) Maybe after collecting 30 sprites her passive also gives a health per second boost to those within, 60 sprites and the effect is boosted then 120 for a bonus effect. And so on. Each Sprite collected can give her a bonus .5 move speed too.

Sona, gets a 3 note sheet added (Example W, E, Q in that order then changed up per sheet), on completion of its order she gains an extension to her aoe effect duration/radius. After hitting say 15 a new note is added to make it harder to complete for the boost, etc. Maybe with every 15 sheets complete she gains bonus mana regen.

Soraka, landing Q gives her a permanent health per second boost and then after 20 hits to champions it reduces the travel time by 10% each time.

These mini games can give gold amounts of 3/6/9 depending on difficulty. Like with Senna farming souls.