Sona Rework Idea
Ok, so Rozair made a post asking about ideas for reworking our mains, but mine got a little wall of text-y and didn't feel quite right for a comment. This is something I've been thinking a bit on and would like to see some (even just a few) more opinions on my ideas. TL;DR at the bottom.
So oh boy, here we go.

The basic idea for what I have is to make a really toned (and I mean really) toned down version of Invoker; I don't play dota, so it's mostly the idea.
For her passive, instead of flat bonuses based on the last spell cast, I would make it's affect based on which 3 spells were cast leading up to it, with the effect varying with number of of casts of each spell and maybe order.
For example, casting one of each spell (a normal combo) would yield all three current passive effects on the next auto, but at maybe half or a third of the current strength. Casting one spell and another spell twice would yield the 1/2 or 1/3 effect of the single cast and near or at live values for the spell cast twice. For a spell cast three times to achieve the passive, the bonus would be higher (maybe 50%) than live values. If they wanna be more in-depth, they could add bonuses based on what number each spell was; the first spell has a diminished effect while the last has an increased effect. This might be a little complicated and Sona should still be relatively newb friendly; I want easy to learn, hard to master.
In order to keep this change in line, though, I have two extra conditions for it. One, stacks building to her passive decay after not using spells. Two, using a fourth spell starts the cycle over from the beginning. The first prevents a Sona from sitting there with two q's stacked, waiting to hit you with a q and a 3-q power-chord q-enhanced auto. The second means she can't get to three q's and then sit there, casting q whenever her passive stacks would start to decay.
The main point of this passive change is to emphasize flow and rhythm, the elements of music. The powerchord should be the culmination of the spells cast to get there. The passive "controls" emphasize not just randomly hitting buttons but flowing through the fight, making sure you keep the spells coming (which lines up with Rito's changes to her ultimate, adding CDR for her normal abilities) and be on point to use your powerchord after the third spell. It also means Sona as actual decisions to make. She could hold off and try for a lot of damage with a 3-q passive, but that means she can't heal or speed up anyone that fight. From a gameplay perspective, I think this last part is perhaps the best element of my idea.
Moving on from the passive, I also have a couple of ideas for her abilities.
First, make the effects fall off with distance; her moves are literally sound and sound dissipates. Video-games don't have to be realistic, but reality is a good base. And when I say effect, I mean for both allies and enemies. You can heal and shield the tank really well or give the ADC a really nice shield; not both. The same goes for auto-enhance on q and the speed boost on w. Sona herself, being at the center, would theoretically get the max effect. HOWEVER, if Riot want so to focus on support Sona, and effectively kill mid-Sona, they could make it so she gets no benefits; I don't know if I want them to kill mid-Sona, but that's a question for another time and at the very least, doing this would making buffing support Sona easier without worrying about mid lane outcomes.
I think this change is good because it again emphasizes flow. The argument has always been that you deserve to die if you let Sona get close enough for her to q and powerchord-lichbane-auto you; these changes would make it even more true. A Sona that "flows" into the fight and get's right next to the enemy AD without dying damn well should be able to kill said AD.
The last change (I promise this is my last idea) would be to take away the "flying" targeted parts of her spells. Now most Sona players would hear that and freak, but hear me out. Instead of a targeted part, the aura part gains the effect of the targeted part as well as keeping it's current passive effect. The range on said aura's would be increased (I'm thinking Karthus whatever ability it is, you know the one, size). Next, the spell itself would flow out in a circle (just like the current auras, but flowing out to get there) instead of being instant; I'm thinking slow enough for someone with a blink/dash to escape or for people on the edge to be able to walk out without getting hit, but fast enough that the average champ can't walk from mid-way to all the way out before getting hit. I can't really say anything on the balance of this, it just seems to fit. For a similar spell, I would actually point to Vlad's new third q (or at least I think it's q, I don't play vlad). More interesting, this would aid mid-Sona by potentially giving her something she sorely lacked; waveclear. That may contradict prior ideas, but their ideas, it happens.
TL;DR Make passive depend on the all the spells used to stack it, not just the last; the spells (notes) build up to the powerchord (sort of the final note for that part). Make the spells feel more like sound, which they technically are.