Just to throw my feelings out there:
I like the way Unending Resolve is right now. A little bit of extra passive mitigation would be nice, but I prefer it being active for both PVP (CDs popped and ready to burst you down) and for PVE burst raid damage phases (I'd like to be useful on Ultraxion fights without having to spec into a very short term mitigation talent, Boomkin and Spriests don't have to trade passive survivability for active damage reduction). The choice between using it defensive and offensively is at the same time problematic and interesting, though.
I know Xel is sick of it but I have to throw my hat into the "Destruction could really use a proc" ring, and I think the most appropriate way is through Fel Flame. Whatever the trigger is, have it let you cast X number of Empowered Fel Flames that will always crit and cost no mana. Helps break up the monotony of Incinerate spam, and helps Ember generation in PVP. Finding a trigger for it could be tricky. Attaching it to Immolate ticks makes dispels hurt. Conflag probably has too much downtime for it. A proc on Incinerate requires too much hardcasting. Maybe the devs wouldn't want more instant casts in pvp? I know Xel has covered this, so I'm not expecting anything of it....just an opinion.
I think a return of Death Coil could work and co-exist with the Mortal Coil talent. Death Coil (or whatever new name it would take) would be like the old baseline spell, while the Mortal Coil talent would exist to upgrade it to shorter CD and greater effect. Though I suspect that with a baseline DC the other talents in that tier may be more attractive instead.
I don't get the sense that Warlock survivability is something they're looking at, but I suppose if this were an issue, an additional avenue to take could be to turn the Stam +Healing bonus from Fel Armor into straight percentage Damage Reduction like Shadowform and bake the Stamina Bonus from Blood Pact into Dark Intent. This would have little effect if you were already running with an Imp out, but it would allow us to use other pets for their utility while not having to rely on others for the Stamina buff.