Theory: Damage Supports are responsible for our current ADC-heavy Meta
So anyone remember a season or two ago when damage heavy supports began to flood into the meta in a really mainstream way?

Most of these champions were core 'mid' champions, and as a support main - I fell in absolute love with the meta shift. The primary reason was because I was sick and tired of being completely dependent on my ADC to carry the lane/game. It's an awful feeling to be supporting a player that your leagues better than - and it was one of my most common league support experiences and I loathed it. I think the majority of players picking up these champions in the support role were looking for an **escape from that type of scenario. **
Once they became pretty widely accepted, you started to see a lot of defensive supports get poked or blown out. Taking a Xerath into a Braum matchup was hilarious. Not only did my beam go through his shield, but the ADC had to manage juking skill shots rapid fire with CSing - I found I could seriously impact my opponents ability to CS by just being a lane threat. My point is that there were a lot of new bot-lane matchups that were terrifying to go into as a traditional or tank support. I think Riot had to make a design decision to combat this new meta. The solution came in the form of tighter mana control and new items for defensive/neutral supports, namely:

They had to be really strong, or the meta wouldn't react to them - And oh boy, they were. They have largely worked, giving supports the strongest tools the game has ever seen to shield and heal a targeted ally. League has never really seen a shift like this. Supports could force a squishy target to survive a potential burst scenario - something that generally wasn't possible before. ADCs, between a variety of summoner spells, support items, and various champion skills have become extremely hard to kill when they are being protected by skilled players.
With this new meta in place, your seeing ADCs become the core focus of the game. They always had the capacity to carry games - that's literally what they were originally designed to do - but now with these new tools, and in this setting - it's harder than ever to deal with an ADC once he gets some lifesteal and someone committed to protecting him.
At a time when all this was going on, Riot compounded the problem by committing to the assassin rework. Peeling back some burst damage in favor of strong mobility. Now Assassins have a role problem, as the ADC has late-game burst, or even mid-game burst, and yet many assassins feel completely left out. Stealth or Mobility are really the only unique tools of the Assassin role/class, at this point - and its a bit of a shame.
And so ... I think the origin of this ADC meta all started with damage supports. Where do we go from here? I see 3 potential paths or maybe a bit of each?
1.) Tanks get a really big buff against ADC-centric damage. This would be another really strong 'mandatory' style tank item that just completely changes the meta - Now ADCS can be protected, but extended skirmishes and strong initiation mean that the frontline has much more impact. The downside here is that mages and mid-lane gets a bit left in the dust.
2.) ADC damage gets reeled in, and more champions and roles get the opportunity to 'carry' the game - in many ways, itemization will start feeling a bit more like DOTA, where 'falling off early' doesn't really exist, and lategame brings about some of the strongest items league has ever seen, just not for ADCs (because they are already there!) Imagine where the term 'Hyper-carry' applies to the majority of the roster, and not to just 'ADCs'.
3.) Support itemization changes in a big way, and the ability to 'shield' or protect another gets hampered in some way, thus making the ADC fragile once again. I'm least excited about this change, as I feel its the most generic - I like metas that shift.