No, there will be no choice. We'll alternate periods of extreme burst with periods of mediocre damage output and hopefully achieve competitive dps over the duration of a fight. There is no announced change thus far that will result in this "sustained damage" spec of which you speak.
That might improve elemental dps overall, but that'll give it the same two glaring problems as retribution (the "wings" issue) and any other cooldown-centric spec. First, the dps of such a spec is overly dependent on fight length. Boss dies right before your next big cooldown explosion? Your dps plummets. Boss dies right after it? You do 15k more overall dps for that fight.
Secondly, such a spec spends the bulk of a burst-centric boss fight dealing horrible damage while saving those cooldowns for a brief moment of glory. Lame again.
As much as everyone bashes the number tweak to Shamanism every patch, I pray we see yet another one (in addition to some other numbers changes and QoL improvements). New or improved burst cooldowns are exciting, but not if we're wholly reliant on them even for mediocre overall dps. It just makes the periods between cooldowns all the more depressing.
I know it'll never happen, but I'd like to see shocks lose the shared cooldown (if not lose their cooldowns entirely) along with a numbers tweak on lightning bolt. And for Lava Bolt to deal greatly increased damage on a Flame Shocked target rather than an auto-crit. Let crit rating mean something for more than half our spells already.