So, I don't know, maybe I'm just wasting my time here, because apparently _not even the interns_ look at the NA PBE. (Still waiting on that Shen Feedback Thread, guys.) But I just wanted to say my piece here, as a support main.
The big problem with Soraka is her lack of counterplay, right? A good Soraka with a good team can carry because she can keep them alive when she's not focused, and they can peel for her when she is focused. She's like a second carry. That's why she's gotten these new nerfs that require her to land Q over and over to maintain her heals. Making her move out into the open introduces counterplay, so that assassins can kill her.
This was less of a problem a few weeks ago, because you could build Grievous Wounds to mitigate a pesky Soraka's healing. Once Grievous Wounds got reworked, people couldn't build against Soraka past the drafting phase, and her banrate in high elo skyrocketed.
So why don't you just make it so that her W, and maybe even her R, don't heal as much if a target is afflicted with Grievous Wounds? It's the smallest change you could make that would provide exactly what you're looking for.
If you want to take it a step further, you could say she heals less on targets afflicted with certain types of CC/debuffs. What if Soraka's heals didn't work as well on a target who was rooted or stunned? Now there's counterplay, even if Soraka's way in the back line, or on the other side of the map. The target has to keep moving and not get hit by CC, and they're fine. But if they're careless, they can still mess up and get killed.