Well, pre-patch and beta are two different things. Right now in live, assuming you at least have the heroic version of the class trinket, but rotation is literally 3 spells on repeat (taking soul conduit over demonbolt). HoG, empower, shadow bolt. Repeat throwing in your doomguard and service additional pet cooldowns when available. The class trinket interaction with demo is just broken right now, so you want to cast as many HoGs as possible. You don't even cast dogs in this cheese build since there's no chance to spawn extra imps from your trinket there. 3 spells, over and over. That's max dps right now.
The real rotation, which is based all around the cooldown on the dogs is much better obviously, but it's the role the class plays in progression that I'm most worried about. Maybe they'll get buffed and be the top dogs of single target DPS and then on the like 3 purely single target fights we get the whole expansion it'll be a necessary spec, but right now they need more changes than that to be relevant on the other 30 fights. You can talent to do some burst AE while sacrificing your single target dps, but ultimately Destro just does all that better. Once you're forced to target switch, demo, as it is currently, is going to fall behind either of the other specs.
Just to clarify I'm talking about Mythic progression too, which isn't the scene most people are in. I know at Legion release Destro is going to be the best raiding spec of the three so that's what I have to go with. Blizzard always does another round of tuning before the 2nd raid, but my guess is I'm safe with this assumption up through the first tier.
