Some possible fixes
new sight stones
Example, we have an hp sight stone
Now let's get a mans sight stone and an ap sight stone
Part of the reason for their dominance is supports will build sight stone and this heavily favors tank supports because it focuses on one of their favored stats, hp
While ap supports have to build it, and they don't get nearly tanks enough to actually benefit from it
Possible example
Arcane stone, provides 25 ap and gives the sight stone effect, takes 1 tome + combined cost to equal 800g total cost upgrades with one more tome and combined cost to become 50 ap and sight stone effect (5 ward stored now)
Another option is mana stone mana regen item, and combined cost to cost 800g for 200 mana and 25% mana regen and sight stone
Upgrades with one more mana crystal to 400 mana and 50% mana regen (5 stored limit)
And what will keep other classes from not getting these and keeping them? They are at best mid game items at full upgrade and can be replaced with other items to be more effective
Sure a non support could grab this for more vision (which isn't a bad thing) but they are still trading combat power for vision in this case
The reason supports would still get these is because it gives gold effective stats if you use the sight stone effect throughout the game instead of spamming wards