Strategic Diversity and its Items

#And for honorable mentions:

All of the items mentioned above share common theme. They were either:
- Introduced in Season 5 or late S4
- Reworked in the same timeframe
- or always counted towards the goal of
enabling a sense of Strategic Diversity. Now, if there's a term Riot's plans for S5 could be described with, it consists of those two words.
Now, on a champion side, it can be argued that this was a success to some degree. Season 5 competitive sees one of the most diverse champion pools yet, with many interesting picks (mid Kog, mid Varus, top Cass, the return of Urgot, Viktor, Sion, Supportilus) being played successfully.
However, the item side looks differently. Of the host of items described above, only a few are used regularily:

What about the others? Why are they not used more often?

Usable on: Heal/Shield-based Supports Why not used? While the recent overhaul gave it more intrinsic synergy, it is still an item with a very concerted usage range, one that depends both quite heavily on the user herself and the team around her. For the ideal use case, the user should be able to shield or heal multiple allies at once, and said allies should actually be able to make use of the buff, too. For example, a comp of Graves/Katarina/Amumu/Riven cannot make too much use of the item, while a team with Kalista/Rek'Sai/Azir/Irelia would actually synergize with it rather well. What could be improved? If they wanted to make Censer less niche, they could possibly improve the effect on single-target heals/shields (similar to Spellvamp or Rylai's effect). Another possible avenue would be to just increase its AP a notch.

Usable on: AP-using Junglers or Supports; possibly toplaners Why not used? Essentially, it is a win-more item. Buying it doesn't help you if your team is behind and too weak to siege, but it can be a rather strong tool if you're already ahead against a magic-damage based waveclear comp - especially when combined with Baron'd Cannon minions. However, it is less useful if the enemy has long-ranged physical damage. What could be improved? There are certainly ways to buff BoC - for example, lowering its combine cost a little or give it like 50 more HP. However, I am not entirely sure if it actually NEEDS a buff - you can even see it in competitive sometimes, although not as often as I'd like to (in comps where it would be perfect, for example against Ziggs/Corki teams).

Usable on: Top lane splitpushers, siege comps, even some ADCs Why not used? Honestly, I have no idea. Oftentimes, when I see teams base after getting Baron to prepare for the inevitable siege, I ask myself: Why not get this one? Especially if they have no or only one source of ranged tower damage and/or BoC.

Usable on: Mana-intensive ADs who also auto-attack regularily
Why not used?
On almost everyone, it is simply inferior to its competition,
.
What could be improved?
First off, I don't think adding a baby version with its passive would be a good idea - easy access to that kind of sustain in laning, and especially early in laning, has the potential to break several champions (
, among others). However, it could definitely use a bit of an easier build path - with
being a common suggestion. Another avenue could be to keep the build path difficult, but reward the user more for completing the item - meaning, buffing the item's final stats. For example, by raising the Lifesteal to 12 to 15%.

Usable on: Top laners, mostly. Ain't no towers in the jungle.
Why not used?
Similar to Reaver, it is simply outclassed as an item. Its alternatives,
and
, are just giving way better stats, as well as less situational passives/actives.
What could be improved?
It would be great if its stats were raised a notch, even if the item was made more expensive to compensate. Another great change would be to give it an effect on allied turrets, too - like the old Summoner Spell Fortify (except only affecting the closest tower, of course). Like, giving the target tower 33% to 50% damage reduction, instantly warming it up, increasing its shot cadence, giving it splash damage or multitarget attacks or even having primarily target a marked enemy champion, possibly with bonus damage.
Usable on: ADs of all colors. Top, Jungle, certain mids, even some ADCs.
Why not used?
Well, actually, it is used quite some in solo queue. In competitive, there's just the "problem" that AD champions are not particularily popular currently - and if they are, they make better use of Trinity Force (
).
What could be improved?
If it absolutely needs an improvement - and I am doubtful about that - they could reduce the number of stacks from 6 to 5, while retaining the 30% max shred. Sometimes, I feel that champions run out of steam to capitalize on the applied stacks.

Usable on: AP-based supports Why not used? There are better (or, rather, more necessary) buys for an AP-based support, especially early in the game where the active would have the most impact: A damage focused support like Zyra would get Liandry's or Morellonomicon, whereas a more supportive support would get something with mana - usually Crucible. How could it be improved? I think that Twin Shadows would benefit a lot from going back to something more similar to its release version: On release in S3, the item build out of a Null-Magic Mantle and Kage's Lucky Pick (AP gold generation item), and gave MR/AP/MS and the active. Especially since Riot is looking for a new AP/MR item to go along with the reworked Abyssal.

Usable on: Certain (AD-based?) supports Why not used? Horrible build path and sub-par stats for a support. Sub-par stats for a jungler or top laner. Needs a team with several champions who'd benefit from the aura, and who also fight in close proximity to the owner of the Herald. How could it be improved? Full-blown rework. And I honestly have no idea where they could take the item, too.

Usable on: Theoretically, any champion with a lot of HP or strong sustain. Practically, probably the top laner or the jungler. Why not used? Difficult question, imo. Probably has something to do with the weak-ish build path (Raptor Cloak is not the most useful of buys for the amount of gold - this also goes for Ohmwrecker). Possibly, also the static nature of the Portal in the mobile game of today. How to improve it? I am very much against increasing its stats further - it already has a rather strong stat combination (there's a reason only two combined Armor/MR items exist). I'd rather see them do something with the active - like, reducing the CD to 120 or even 100 seconds, but restricting the number of active portals to one per person. That way, someone could use a portal to set up or counter a medium-sized slow push on a lane and walk away to do stuff with his team, and then use the portal again when the real sieging work begins.
This was my opinion on the current problem children in the itemization for strategic diversity. Do you agree/disagree? Why?
Or do you have different ideas on how one of these items could be improved?