I'm definitely interested in that build.
I think outspeeding Mega-Luc is a good idea with Meloetta-P. Sure they'll probably go for priority but you can take that at a high enough health. Close combat is a different story, though so it's probably good to be safe against him. That also isn't too much more speed than outspeeding 110's anyways, which would be another good benchmark. 128 with a Jolly nature should accomplish that, with the rest being able to put in HP, but I'm looking into seeing if that extra 128 adds any relevant 2hkos to special attacking coverage, with Thunderbolt being my main curiosity. Switching back to Meloetta on Gliscor/Landorus and other physical walls or intimidate users also seems like an interesting option.
While the sleep chance isn't the part of the move the build relies on, that 20% chance is brutal, and if you can be firing off 2-3 a match you're going to see a lot of sleeps. While less likely, it's the most crippling scald ever, which is a nice touch to an AV user. I like it.
Here are some interesting calcs for 128 Special Attack Meloetta P and Meloetta for one using Relic Song/Thunderbolt alongside drain punch/knock off
128 SpA Meloetta Thunderbolt vs. 4 HP / 0 SpD Gyarados: 356-420 (107.2 - 126.5%) -- guaranteed OHKO
128 SpA Meloetta-P Thunderbolt vs. 4 HP / 0 SpD Gyarados: 248-292 (74.6 - 87.9%) -- 87.5% chance to OHKO after Stealth Rock
With thunderbolt you lose less immediate coverage against ground/flyers that would wall your set, but relic song is an interesting option for that while gyarados is a very scary thing to give a set up opportunity to.
Thunderbolt turns you into a really good way to protect your rocks from the premier defoggers of the meta.
252 Atk Meloetta-P Knock Off (97.5 BP) vs. 4 HP / 0 Def Latios: 252-298 (83.4 - 98.6%) -- 68.8% chance to OHKO after Stealth Rock
252 Atk Meloetta-P Knock Off (97.5 BP) vs. 4 HP / 0 Def Latias: 228-270 (75.4 - 89.4%) -- 12.5% chance to OHKO after Stealth Rock
128 SpA Meloetta-P Thunderbolt vs. 252 HP / 0 SpD Skarmory: 164-194 (49.1 - 58%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
128 SpA Meloetta-P Relic Song vs. 252 HP / 0 SpD Mandibuzz: 79-94 (18.6 - 22.1%)
128 SpA Meloetta Thunderbolt vs. 252 HP / 0 SpD Mandibuzz: 186-220 (43.8 - 51.8%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
if you see the Mandibuzz switch coming in on Meloetta, you can go for a relic song/thunderbolt combo and leave mandibuzz hanging on for dear life if they went for the defog.
You don't have much for Scizor, besides relic songing for sleep or maybe trying to win the fight with drain punch, but a lot of defog scizor are going physically defensive now so that's a losing battle.
This is all made much better if these pokes are switching into Meloetta or Meloetta P. I'm not sure how often or easily that can be set up with rocks out now.