The current success of the Death Knight as the first hero class has made me quite optimistic that future hero classes could possibly thrive in the game. The death knight has its appeal stemming from the fact that it's something new and fun. Its potential as a killing machine can be reached without much effort, making it pretty user friendly for people who want to try it out. It's also different in the sense that it's made dual wield tanking viable and joins the feral druid as another class/spec that tanks without a shield.
As someone who found the joys of healing (something I thought I'd never do if you asked me in vanilla-WoW) while playing a holy paladin in TBC and currently plays a restoration druid, I would really love to see the same brand of innovation and appeal applied to a healing class. Shortly after Blizzard announced the death knight as a hero class, I always wondered about the possibility of a healing hero class. Later on after learning about the death knight rune system, I actually expanded that thought to the possibility of a healing class that doesn't use mana at all but something different just like the rune system. Apparently these thoughts I've been having are shared by Blizzard's Ghostcrawler himself as shown in his forum post below.
I could totally see several ways to design a new healing class that used mana in a different way or didn't use mana at all. You are right that it might not appeal to players who hate healing, but it might appeal to players who just haven't found a class that heals in a way that is fun for them. source
The most obvious problem with designing a healing class that doesn't use mana is that mana is center of what healing is currently about. Intellect, spirit, and mp5 all have something to do with mana and they are important to healers. The corollary to this problem is itemization since healing gear across all armor types use these stats. the only way I see this problem being solved is to design a system that translates these stats to affect the new resource system
Ghostcrawler mentioned something about healing in a different way than the current healing classes do. If they did implement a new healing hero class, it would certainly have its own style and niche and that's something I'm really excited to see in the future.I know that we're all supposed to be focused on the current expansion but Ghostcrawler's thoughts are already getting me excited and hoping that this idea gains some steam.