I've put a lot of thought into this rework before I decided to say anything about it. Most of my time I have spent playing support characters such as Sona.
When I read the rework I was excited that things were going to change. To be honest every serious 
player knows that she is AMAZING (pre-rework) and with just a little tweaking she would have been fighting with 
and 
for THE support character. I would have to say that this rework is more like a nerf.
Here is the breakdown:
From the start of the game, Sona works best operating close to her allies. Here her auras help them trade effectively, with Hymn of Valor boosting her marksman’s attacks while empowering her own poke.
With longer cool downs poking is much less effective. Having to wait longer to keep the damage on. Not to mention the fact that smaller range makes poking much more dangerous for the uber squishy etwahl player.
Aria of Perseverance heals more on low health friends, so while topping off an ally’s health is relatively inefficient (particularly with its high mana cost and low base values), saving her heal for later in fights grants markedly more health and makes baiting all the more effective.
Though big heals are nice, but at what cost? Baiting will be a newer tactic for some Sona players. The issue with this is being a bigger part of her game play is how squishy she is.
Power Chord offers some tactical options, too: Aria of Perseverance’s Power Chord effectively reduces the enemy marksman’s attacks when timed correctly, while Sona can chase down fleeing enemies or escape from ganking junglers with the slow from Song of Celerity’s Power Chord.
This is just not good enough compared to what you took away... You want us to put the porcelain doll in the middle of it to do this.
In teamfights, the smaller auras encourage Sona to stay mobile enough to heal, shield and empower her allies as needed.
Smaller auras encourages lots of grouping.
Song of Celerity gives her plenty of movement speed, and tagging allies with the edge of her aura gives them the same buff while extending the duration of her own. And while she previously relied on flash to position for her ult, her new E’s sudden surge of mobility is significant enough to get Sona into position to use Crescendo, which is just as potent and game-changing as before.
Watch that video. (^ You guys already went over this ^) Really though. You lied right to our faces. "She doesn't need this... watch me do it though" T-T Come On Riot!
Once it’s been cast, Sona works best healing and shielding her squishier allies with Aria of Perseverance while using Hymn of Valor to amp up her allies’ damage.
So, continue to do what you do at this point.
That means Nothing has improved in Sona's team fight either.
So what’s changed? Well, Sona’s gameplay now revolves more around moments of power. Instead of hanging back and winning a war of attrition during laning, Sona’s now got the kit to power up her allies and save their lives when a fight turns against them. Auras are smaller and more visible now, so getting the most of them requires great positional awareness for Sona and coordination with her allies. This allows us to reward great play with much more impact for each of her songs. You’ll be able to make plays as Sona, earn your team kills and save lives with clutch ability casts and smart positioning. At the same time, the enemy team has larger windows to fight back in thanks to her longer cooldowns, adding in clarity and counterplay to Sona’s kit. We can't wait to see what players can do with her update.
Without the ability to hang back, Sona is pretty much useless. She can't afford to get close enough to do anything when it isn't absolutely needed so when she does get close, she becomes target #1 and has no chance of making an impact, due to squishy-ness/longer cool downs. The new counterplay to Sona's kit is: "Wait until she does something, then kill her..."
I need a new character now. =(
