The Core Problem With Jungler and Support Items...
... is that they're designed to cater to classes that are expected to run on lesser gold gains, which means they're inevitably going to offer relatively cheap power. The moment those items become cost-efficient enough, they get abused by laners, who get to reap the benefits of their cost efficiency without any of the associated gold/exp restrictions, which makes it hard to keep them balanced for everyone.
(Also, massive wall of text below, TL;DR at the bottom)
The current solution for jungler items has been to make their power more jungle-centric and/or make them near-identical to an equivalent laner item, but that just means half the current set of jungle items ends up being "junglified" laning items, which isn't all that bad (Cinderhulk and Runic Echoes/Runeglaive are fun items) but not really as diverse as it could be.
The current solution for support items has been to flat-out reduce their power, as is the case for Frost Queen's Claim now and the other two lines during the preseason patch, which takes them out of solo lanes but ends up harming supports most of all. The issue with these items being too powerful or cost-efficient is that they're designed to be just that, and it's difficult to add more support-centric power here because practically every stat on a support item can directly benefit non-supports.
Right now, jungler and support items cannot easily be made to feel good on the classes they cater to without being abused by others, and we're at risk of ending up with a whole line of items that feel more necessary than fun (supports already have that with Sightstone, too). Imo, we need some of the following:
- Make champion number differences in lane much more manageable, perhaps even fun, and balance around that: Currently, junglers are forced to be behind on core stats and experience relative to laners because ganks are already terrifying in forcing 2v1 combat. Additionally, any kind of 2v1 lane setup tends to feel horrible to play for both sides, since it forces turtling and makes the outnumbered side feel like they have few to no options. The sort-of-counter to that is gold/exp sharing, but in a natural duo support/marksman lane setup that just ends up with marksmen being relatively unaffected by gold mechanics and supports having to work with little to no CS. While this would probably be really complicated to implement, we need map mechanics in place that allow 2v1 lane situations to give the weaker side more options, at least early on (dying to greater numbers is fine in mid and late game), which could allow supports and junglers to get on everyone else's power/gold level from the start.
- Give support items Cull-style commitment rewards: Right now, it's relatively easy for laners to abuse support items, because they can just skip to the top-tier version and get their full range of bonuses, which means even the relatively mediocre AP on FQC or health on FotM can be too good for their cost. It would probably be worth trying out a Cull/Tear of the Goddess/Devourer-style transformation mechanic where collecting a certain amount of gold via the unique passives would unlock more power (e.g. more stats, new stats, upgraded actives or passives, etc.), which would make support items less likely to be abused (solo laners would have to do duo laner stuff to reap their full benefits) and also potentially far more slot-efficient in the late-game for supports.
- Give caster supports their own scaling path: Right now, caster support item "scaling" usually revolves around building massive amounts of CDR and mana regen, which at best gives them less viscerally satisfying mage stats, and at worst makes them a bit flatter by turning them into near-manaless spambots. Imo, a "traditional" support build shouldn't force supports to have little personal power, it should give them power nobody else would put to the same use: supports like to roam towards warding spots and allies, shield, heal or buff fellow champions, and use lots of ally-oriented item actives, none of which are primary concerns of solo lane mages. Giving stats or bonuses that would cater specifically to those mechanics could allow support items to have more immediate power without becoming too attractive to solo laners. We sort of have that now with Ardent Censer and Ruby Sightstone, but support items could probably go a lot further.
TL;DR: It would be better to make 2v1s in lane fun than to force junglers and supports into less satisfying itemization paths, and putting everyone on similar gold levels would prevent any specific item that's decent on an underfed class to become OP on another. Support items also need stats and bonuses that work specifically on supports, or at least duo laners, in order to feel powerful without being abused.