While it's doable as evidenced by HW, support balance tends to be much more complex than DPS balance. It's relatively common for them to adjust DPS output mid-expansion to fix balance problems, but they seem to struggle to achieve the same from a utility or mitigation standpoint. I think that this presents much the same challenges as adding two tanks or two healers in the same expansion. Perhaps even more so, because their attention will be split and one of those two roles will likely suffer in terms of balance.