Would Discipline Priest Mechanics work in FFXIV?

[Shurrikhan]

(Melee healer concept discussion)

You do not need to redesign old encounters because the gear is worthless from them and power levels are so high compared to when they came out that they are nearly trivial.

This. But, I would argue that you could also equip the new healer style with means of immunizing themselves to these things, rather than causing content to treat them all equally or leaving certain old fights unaccessible to melee healers..

Give them a Veil function, similar to the later half of Warden's Paeon, which keeps them from receiving the next debuff and immunizing them completely to others; give them an ability that draws projectiles from nearby allies to themselves, up to a damage cap, and reduces their AoE radius if any; give them directional barriers, etc., etc. These can all play into interesting parts of the class while making them viable for such raids.

If a melee healer has ranged heals, then it's not really a melee healer.

A "melee healer" as a term to describe certain healers across multiple MMOs has usually just meant that some part of its toolkit is limited to melee range. This can be just its filler dps, just its AoE heals, it could be short-range auras, etc.; it doesn't have to be everything, or even all of its healing abilities. It just describes in what range the healer would typically be standing, for a fair bonus, not that it can't move out a bit (albeit likely at cost).