Putting the tank debate to the side, something I see we haven't exactly covered is healers.
As we all know, White Mage has been the sole healing job in Final Fantasy since pretty much the beginning of the series. Others have been introduced or tweaked throughout the years, or healing was spread around to allow better balance (Summoners in FFIX having access to White Magic, Dancers in FFXI being able to heal), but the constant has been White Mage.
Much like with tanks and DPS, we need a healer roster, as funneling all healing into one job is not smart on the long run.
The main problem I see is that White Magic is pretty restrictive, specially when taking the job description for WHM into account. Looking at how healing is done elsewhere and how it is spread about in a way that gameplay varies per class but the result is the same (which means that all healers should be able to perform equally or near equally in all content), we might be able to expand the healer pool in a way that makes sense without taking anything from White Mage.
Looking at how healing is approached in MMORPGs, we know the following types of heals exist:
- "Traditional" heals: Single-target and group heals that have to be cast and heal allies for a set amount.
- HoTs: Heals that take place over time as set values over X seconds (unlike FFXIV's and FFXI's Regen) and are usually instant-cast.
- "Smart" heals: Heals that are set to hit X number of targets, always prioritizing the party members with the lowest HP.
- Heal Auras: Recover a small amount of HP per tick for everyone in range.
- Heal "Zones": Laying an object or marker on the ground, causing anyone that steps in the zone to heal while the zone is active.
- Transfusion Heals: Deal a small amount of damage or hinder the enemy's resources and apply a multiplier that heals party members.
- "Attack" Heals: What would be your regular attack can be used to heal a target party member.
WHM is (and should be) built around traditional heals. You can really add whatever you want for utility and so on, but at the end of the day the job is a healer built around spells that have to be cast and heal for certain amounts. With that in mind, we can have healers that focus on or use the other heal types as part of their arsenal, with a traditional heal somewhere in there as filler.
Some examples of what I'd like to see:
Green Mage: Emphasis on HoT's, with possibly a smart heal. Can do whatever with utility.
Chemist: Emphasis on attack heals (CHM with a pistol or a shotgun that shoots pellets filled with healing salve?

), heal zones and a traditional single-target heal. Can do whatever with utility.
Oracle: Emphasis on transfusion and smart heals, with maybe a HoT. Can do whatever with utility.
Of course, status removal and ability to raise would be available to all healers. Can't have a healer that can't cleanse debuffs and raise the dead, after all.
---------------
Before the "if this wasn't in FFXI we don't want it" brigade comes in to (try to) shut me down, we really should stop to think about mechanics and playstyle differences. Much like tanking, different people are drawn to different types of gameplay for healing. Some may be drawn to spreading HoTs, some may be into smart heals or transfusion heals. I personally hate healing, yet attack heals found their way into my heart to the point I am willing to heal a group if the healer roster has a class built around that mechanic. Just goes to show variety is a good thing, and may help in putting groups together.
Questions, comments, flames, death threats and so on are welcome.