In 10-man Ulduar, GC expects that we'll want to bring three healers, and claims that they "intend for you to be able to take any 3 healers." This means that even smaller guilds with only enough players to form a 10-man group will be able to work with the healers they have, rather than feeling the need to recruit specific classes.
In 25-man Ulduar, Ghostcrawler mentions that there will be "more pressure to have every player in the role that most emphasizes their strengths" and that we'll "want a mix of healers."
This sounds like a fairly flexible plan, allowing for groups to recruit different healing classes, and allow healers to spec into different roles, such as group healing vs. single target. It also suggests that Blizzard is not planning at this time to homogenize the healing classes any further, unlike the tanking classes.