If you're going to go through with this nerf to Soraka...
Then you NEED to reduce the health cost on Astral Infusion, or give it a scaling health cost based on rank. The whole idea behind Soraka's rework was so that she could be a dedicated healer, without mana restraining her but also without being too good at it via health cost.
#Starcall (Q) mana increased to 40/45/50/55/60 from 40 at all ranks #Astral Infusion (W) mana cost increased to 50/55/60/65/70 from 40/45/50/55/60
Like, I get it. Soraka's more frustrating to play against with these changes. Starcall costing 40 mana at all ranks was very questionable, and it also became an ability to max first, for me anyway. She needed a nerf. But let's not forget, Soraka doesn't get as much health back from Starcall unless she has Warmogs and 3k health, which is not my preferred build. She also gives less healing upfront, unless Starcall is active on her, but even then maxing Starcall first leaves Astral Infusion feeling disgusting without Starcall active because of its health cost and low healing until you start ranking up Astral Infusion. If you're going to go through with these changes, then Astral Infusion NEEDS some kind of adjustment to its health cost.
Originally, Riot had the idea of reducing its health cost to 8%. That's fine, or you could make Astral Infusion cost 6 / 7 / 8 / 9 / 10% of her health. These changes are punishing Soraka for doing her job as a healer, when really, I think Soraka's main problem is that she has a constant, reliable, powerful slow attached to Starcall now, along with its 15% movement buff. If I had a choice, I'd get rid of the 15% movement buff and replace it with the original idea of giving 60+10% ap over x seconds. Only then, would I be fine with her upcoming nerfs. I know I'll get downvoted, because a majority of players hate Soraka, but this champion has been my main for 6 years. I'm passionate about Soraka, and I want her to be viable and fun for both myself and the enemy team.