I like the idea of an alchemist healer that tosses around healing potions that poison the enemy. Mix it with the vampire healer idea, but instead doing poison damage makes his potions regen faster or dealing damage heals you and nearby allies? Throw in a shotgun weapon that's basically a bunch of needles that drain enemies and recharges his potions and I've think we've got something original enough to not be similar to any other characters. Heck, we could have two characters here: the alchemist and the shotgun vampire healer.
My biggest problem with Overwatch right now is that there aren't enough dedicated healers. You have Mercy, who's indispensable thanks to her rez but not super fun to play (Especially if the enemy has a good Winston), and Ana, who has a lot of counters and very little mobility. Zen is a DPS pretending to be a healer and Lucio is... Well, he's Lucio. More variety in the healing front would be amazing, and some tanks and DPS with team healing like Soldier's biotic field would be nice. Taking out a healer won't cripple the team so badly if more non-healer characters could share some minor heals. There may be a need to balance that out, such as having more characters that can counter healing effects (Maybe not to the degree Ana does), but it'd add some much needed variety to the roster and make having a 2/2/2 team be less critical. The game needs more hybrid heroes (If any of the current heroes can even be considered hybrid).
After we get more healers, we need more tank love. Orisa hasn't really found her place outside of the moon level, so the roster of chosen tank heroes feels like it hasn't grown at all. The fact that nerfs tend to hit tanks the hardest doesn't help either. I've yet to see a DPS nerfed to the extent Roadhog, Ana, or Dva was. In fact, DPS tends to see buffs (Soldier, Reaper, Sombra, Junkrat, Symetra, McCree, Bastion). The buffs and nerfs are no doubt necessary (Except Bastion - WTF were they thinking?), but as the lead developer has stated perception plays a huge role in the community's behavior. The perception is that DPS is king.
I just want them to stop with the new DPS for a while. If you played with a team of randomly chosen heroes chances are you'd have about 1 healer (And a 50% chance of it being an off healer), 1 - 2 tanks, and 3 - 4 DPS. They try to cover it up by splitting the DPS into Defense Heroes and Offense Heroes and Symetra, but they're the same. It's no wonder most players still prefer playing DPS: Even though the system is geared towards a balanced 2/2/2 team, by sheer numbers it's presented as geared towards a majority DPS team. Additionally most healers have a relatively low skill ceiling and aren't very engaging to play. It's the weakest aspect of an otherwise stellar game.