After some recent nerfs and changes Warlocks fell off and there is no Warlock spec performing really well at the moment. You can make them work but their performance is average at best.
I was thinking on few QoL changes that are actually rooted in old expansions.
Let’s start with Affliction. The main issue is casting UAs with the amount of interrupts and micro CC. Holy Priest being meta healer makes it even worse. So what’s the idea. Add a 2nd choice option for Soul Swap that removes CD but makes it cost a shard. This way you can spread or maintain dots easier. The shard cost would make you sacrifice burst for sustain damage and won’t ruin already existing PvE builds. 2nd and more controversial change is bringing back Soulburn + Soul Swap to apply all dots to the target (UA, Corruption and Agony). I’m not sure if this won’t make you do it every time and then hard casting UAs obsolete but I think it would expand the comp options for Affliction outside of Assassination/Affliction/H Pala.
The QoL for Destruction would be bringing back the option to Soulburn instant Soulfire. Since both spells cost shards you sacrifice Chaos Bolts for it so it’s not a big deal but have easier time buffing Incinerates with Soulfire.
For Demo - not sure if anyone plays Nether Portal in PvE but for me it feels that it’s too similar to Tyrant. Maybe bringing back Decimation Bolt but a bit weaker to enable Demon Bolt build again would be interesting. It has to be an alternative to the current builds and if it had fixed % of increased damage and 2 guaranteed Demon Bolt crits for 150 k it would be fine. Right now with all talents Demon Bolt hits around 120 k if it crits.