Serpents embrace said this, below:
The main reason she doesn't feel rewarding in lane is because of the Q range nerf and the slightly lower damage it has from before. 10/20/30/40/50 off the base IIRC - and it doesn't seem big but it adds up.
That's the kind of difference I'm talking about, here. Keep the live values on her 5-man-nearby auras, and (these numbers, for her damage), add on + 3 / 6 / 10 / 13 / 16 per ally who's not nearby.
I doubt that would be enough to give away a bait, but it would make sona feel slightly better in lane, I think.
There'd need to be a very clear visual indicator of what counts as nearby, then, or it'd be a very confusing mechanic.
I haven't ironed out exactly what I'd want from this, but I was thinking that, while there should be a mouseover to display the circle, it should essentially conform to, "If your screen is centered on Sona, if they're onscreen, they're nearby." If you wanted to put a number value on it, perhaps the max range that sona can tag someone within (speedboost included) if she uses her ability now. So an, "if you can tag them, they're within range." Sure, this would create a couple weird scenarios with allies who are walking away but are in range when she triggers an ability, giving it a weaker bonus, but I tend to think those would be pretty few and far in between.