Nourish and Healing Touch are just taking up unused space on my bars. I haven't used Healing Touch outside of Nature's Swiftness since vanilla, and I haven't touched Nourish since the patch. Both of them take way too long to cast to be worth bothering with, and while Nourish is very efficient, mana is not at all a concern at level 80.
My typical healing rotation begins with a 3 stack of Lifebloom on the tank, after which I blanket Rejuvs on the raid and use WG on cooldown. I will Swiftmend for Efflorescence if I anticipate damage going out to a grouped section of the raid. If someone needs healing faster than Rejuv can handle, and my Swiftmend is also down, I will cast Regrowth. That's pretty much it.
Nourish is ONLY good in its current iteration to refresh LB. Sure, you could just instacast LB but why? You aren't doing anything anyway.
If you're "not doing anything", you're doing something wrong. With the change to Rejuv's duration, even in in 10 mans I am constantly GCD locked; you should be keeping up Lifebloom and Rejuv on the main tank at all times, you should be keeping Wild Growth on cooldown at all times, and you should be keeping Rejuv blanketed on your raid intelligently and as much as possible. Even if your entire raid is at full HP, if you anticipate a target to be taking any damage at any time in the next 12 seconds, you should have a Rejuv on that target; druids' strength is their proactive healing that bridges the gap between damage taken and the time you and your other healer(s) have to react and cast. If you have time to cast Nourish, you're either in a 5 man, a situation where there is no raid damage going out at all, or not taking advantage of your proactive heals.
HDW10: Put everything on the dragon. Use EF on CD ON the dragon. Keep LB rolling on her with nourish refreshes until the portal, where it will bloom. Try and pop off an extra LB cast and pop SM on her when heading in.
I especially wouldn't use Nourish here. Nourish is an incredibly low HPS heal, and you are not at all limited by mana in this encounter; both Regrowth and Healing Touch do significantly more HPS than a Nourish cast, even accounting for the GCDs lost every Lifebloom refresh.