But Eye for an Eye is categorically NOT mandatory for healers. Why do I say that? Because not all healers currently have access to it. It's also a long cooldown short duration defensive buff. It's something that can be done without as every AST can attest to. Much like Virus, it's a "nice to have" not an essential tool for the role.
I'll even go so far as to say Protect is not mandatory... if you don't care about bolstering the survival of your group with a powerful long term buff that can be reapplied at any time. But I'm willing to bet most healers would agree that a healer who isn't able to apply this buff to their group is missing an essential tool (assuming a single healer, statics with two healers can obviously coordinate). But I do remember several times people were not happy in my groups when I was a lowbie SCH and didnt have protect as my first cross-class skill (cleric stance was more important at those levels so was first, protect was next).
But Esuna? That's mandatory. Any healer who can't remove debuffs is a healer who can't fully do their job. It's why Leeches not being unlocked till level 40 was a sticking point for many scholars. The impact is less noticeable at lower levels but still felt. It's felt far more in the later levels.
Swiftcast is basically a given because of the insanely long cast times of the res spells. Were res spells made instant by default I would absolutely move Swiftcast to the optional category.
Lucid Dream is mandatory. Every healer needs a way to self sustain their MP, assuming they aren't the type to stand around doing nothing when no one needs healing. And considering how big a topic thats been and especially with the change to Cleric Stance, I think many players are going to expect more uptime dpsing out of healers in 4.0.
So Esuna, Swiftcast, Lucid Dream = things no healer should be without. Protect is arguably just as essential since its a powerful buff that applies to the whole group and can be kept up indefinitely. In 8 man statics that have 2 healers sure one of them could swap in something else, but in general, I think most people will expect healers to have Protect.
If Affection turns out to be a revamped replacement for Divine Seal, I think many healers will be hard pressed not to take it for those big tank pulls or those umber "oh crap!" moments. But I will concede that even if it is Divine Seal, it is something that one could live without... grudgingly.