Itemization niches that are lacking or missing for S7
It's nice to see assassins and supports getting an abundance of more items on the PBE but riot should take the preseason as an opportunity to create more items that fill in large gaps that haven't been filled in a long time.
Armor + AD
There will be 3 different ways to build MR + AD (Edge of Night, Maw, Scimitar) in season 7 but there has been zero Armor + AD options ever since Atma's Impaler was removed from the game. There really needs to be an anti physical damage equivalent to Edge of Night, Maw and Scimitar.
AD Zhonya's
When Zed, Talon or Rengar come to kill you, your options depend on who you are. If you are an AP champion you build Zhonyas and you can survive momentary burst damage. If you are an AD champion there is no equivalent and there should be some AD + armor item that fills this niche.
MR + HP
For Armor + HP options we have Randuins, Deadmans Plate, Sunfire Cape, Knights Vow, Ohm Wrecker. With the loss of Locket and Banners Command as MR + HP items - not that they were particularly good ones - the only choices for MR + HP are Spirit Visage and Banshee's Veil. This limits your options against a heavy magic damage composition as it's virtually impossible to get high MR while it's easy to get 500 Armor.
Attack Speed + AD
For CDR + AD we have 6 choices in Deaths Dance, Essence Reaver, Black Cleaver, Ghostblade, Maw. For Move speed + AD we have Ghostblade, Duskblade, Edge of Night, For Attack Speed + AD we have Botrk (overpriced at the moment) and that's pretty much it. Rageblade is a useless mess. We really need more items to fill this niche, perhaps bring back the old black cleaver (AS + AD + Armor shred).
Attack Speed + On Hit + Defensive
Right now we have wits end which is a decentpick up on Kogmaw and Warwick and no one else. We really need a physical on hit attack speed item that steals armor. Something like 40%AS, 42 on hit physical damage, and basic attacks steal 10 armor per attack.
AD + AP
For Armor + MR we have ZZ'Rot, Gaurdian Angel, Locket, Banner of Command For AD + AP we have Gunblade, that's it, that is the only item for Hybrid champions to build - Rageblade is a mess and only Kayle is able to make use of it. We really need more options here. Would be nice to have the option to build something besides Gunblade every game on hybrid champs.
Armor QSS
When Malzahar Ults you, you have the option of an item like QSS or Scimitar to help you out. When Riven or Irelia stun you, you have the choice of dying, hoping your ally uses cruicible on you on time, or you need to build an MR item to help you survive against physical damage which is not an ideal scenarior. There should be an Armor QSS equivalent that serves a different niche - perhaps it could be the Armor + AD item I mentioned early on.
Feel free to add any more item niches you think are missing or lacking

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+600g = 3300g
is one of my core items on 
Faebane
Grants 40 attack speed, armor, OnHit magic damage AND-
Cold Steel: Your basic attacks steal 15% of the target's Base Attack Speed for four seconds. Attack speed can be stolen from multiple targets, but you will only gain the highest value.
Grants IAS, HP, OnHit magic damage, AND
UNIQUE passive: Your basic attacks release a chain lightning that applies OnHit effects on up to (number) nearby targets.