Destro is in a really bad spot and I don't mean its numbers directly. For starters it has no hope of aoe via MF when it only impacts RoF. If it can't get F&B included in MF its not going to be a raid spec. Right now destro is crazy behind aff/demo on ptr (like 25-45%) in even near bis T15 gear. It catches up for the most part single target with 4xT16 + amp + crit proc trinket but even then its only getting even with where aff/demo are now.
I saw best results for aff with amp and the haste w' stacking int. Tried full haste and 9778 > haste w' mastery and liked it more. Theoretically with the nerfs to MG/DS and buffs to haunt mastery should be better with haste slightly down. The set bonus makes crit not suck for aff but even with super low crit I saw approx. 70% uptime on the buff. Since aff now rocks aoe with MF it could be a one size fits most spec. AV with aff would mean a double darksoul execute.
You could probably have a crit > mast > haste setup and roll demo/destro provided they ever fix destro's damage and aoe interaction with MF. Aff is still going to be a haste/mastery centric spec. UVLS might hold you through normal modes but sooner or later you'll probably have to make the jump to 5.4 trinkets. With the glyph of EA going away you will need far more regular UVLS procs or the whole system collapses. Right now I think you'd need a double upgraded thunderforged heroic UVLS to have that kind of odds and even then its still RNG.
I'm really hoping destro hasn't seen a numbers fix yet. I know mages are their favorite nukers but really destro could use a look. So far it seems the amp trinket carries destro harder than UVLS ever carried demo which is a disturbing situation that needs a look before live.