Personally I feel, sona's identiy is in the aura effects of her abilities, she is the bard archetype. The rework sort of ripped that identity away from her and replaced with one time, short duration buffs. I personally wouldn't mind if her personal power was lessened greatly to give her just more powerful aura abilities rather than these one shot buffs. She feels really close to a magical Udyr in all you want is CDR so you can cycle through your abilities as fast as possible and weave in the correct passive enhanced auto attack for the situation rather than playing the right song for the situation to buff your allies.
Bards have never been notably strong without their team for them to support. They are buffers/debuffers who use their skills to control and support zones for their allies.
http://www.d20pfsrd.com/classes/core-classes/bard
Role: Bards capably confuse and confound their foes while inspiring their allies to ever-greater daring. While accomplished with both weapons and magic, the true strength of bards lies outside melee, where they can support their companions and undermine their foes without fear of interruptions to their performances.
Imagine if Sona had almost no solo power, her empowered auto attacks rather than being per spell cast, maybe we could have her be more like Dota 2 Invoker. The order in which her spells are cast matters, rather than how fast they are cast.
Her Q rather than being a nuke, is a larger AoE that like her old Q (pre rework Q) gives her allies combat stats aswell as gives all her allies and herself the one empowered Auto attack (new Q Aura).
[I thought of maybe making the AoE burn enemies or interact with them somehow so it isn't 100% a support skill, but the burn would be disruptive in lane if it is like sunfire cape, and i cant think of a thematically strong debuff to go with this skill. even skill name wise, Sona doesn't feel like a debuffing kind of character]
Her W upon activating would be a small burst heal and shield to all allies inside, aswell as create a field around her that provides HP regen.
Her E should just be reverted to her old E but add the AP ratios to the MS buff
[Maybe add an AS/CDR buff that doesn't effect her]
I'm not sure if i'd want to change her R, but an idea would be to make it consume power cord for augmentations (further pushing the invoker parallel)
Edit: I just realized someone else already suggested an invoker style, i think for a music theme it might fit well, though i can understand the 'accessibility' argument.