Healers got fewer changes than most specs in 7.1.5, both because we agree that healer balance has been quite solid in Legion, and because they'd already been subject to some tweaks in 7.1. As 7.1.5 develops, especially with all the new sets, trinkets, and legendaries coming into play, we will continue to monitor whether any further balance tweaks are needed, including to healers. Healer diversity in early Nighthold days has been pretty healthy.
Something yet to be seen is whether this forum (and its counterpart on the NA forums) can be place for slightly more prospective discussion than usual. For example, about potential but not fully decided directions for changes, or as yet unresolved problems or dilemmas, without jumping into a heated argument about (usually) immediate-term class balance.
One thing we'd like to look at at some point is how Discipline interacts with mana, and relatedly how they spread Expiation
s. Among other issues, since Discipline's healing is a product of Expiation
s out and damage done, the best way to optimize total healing over an encounter is concentrate the most possible damage and Atonements into a short window, with periods of low healing or near-inactivity in between. This is both a pretty inflexible healing profile, but also makes Discipline extremely sensitive to added mana in raids. This all also plays into the skill-floor issue that OP alluded to.
Possible avenues to look at would be making a higher portion of Expiation
applications limited by cooldowns or charges, with the high-cost unlimited mana dump option being less prominent. The goal would be to have Expiation
s spread a little more evenly across time and make the spec more about managing them in an ongoing way, rather then occasionally concentrating large bursts of mana expenditure into huge bursts of Expiation
healing. Other goals on Discipline would likely include improving the ability to work in tank healing more naturally while using Expiation