I think Disc's problem is that even though Blizz tried, it's still primarily a tank healing tree. Its raid healing comes somewhat through PoH, but mostly through single-target Penancing or Inner Focused Ghealing.
Holy has a few small problems tank healing, but can just place a Lightwell to do literally ALL raid healing for a bit. We'll definitely see a few minor disc buffs though, I reckon - mainly to AoE healing, though I wouldn't be surprised if they'd also throw a buff to Atonement/Archangel.
At the very least they could fix the innate ~2 second lag on Archangel. Right now, if you have 4 stacks of Evangelism, launch a Smite, and use Archangel as soon as it launches, you get a 4 stack Evangelism > Archangel and then proceed to end up at one stack of Evangelism. It's terrible, though I guess not as horrible as Holy's not-Renew-refreshing Renew-refreshing single-target heals in Serenity Chakra.