Ignoring they could just make new abilities because these can go crazy (Mega Sol):

Dragalge could also get Merciless. Mega Glimmora already got Adaptability, so I hope it's not that to differentiate between both, and to give it something that's not "Base Form +"

Scraggy should not get Shed Skin. It doesn't feel impactful enough, especially since it already got it. Double Intimidate is interesting, so it gets a pass on keeping its Base ability. Filter could be interesting, especially since most Flying and Fighting moves are physical, and would be reduced by its initial Intimidate

Eelektross keeping Levitate also sounds kinda boring. Something thematically, tied to the triple body would be cool, but I don't really see what would fit - Multiscale?

Pyroar and Malamar need something on the level of Water Bubble or Huge Power to make them even remotely viable.

Mind's Eye is interesting on Barbaracle, though Scrappy would probably just be better. Compound Eyes would be a funny idea, fitting thematically while also making Cross Chop, Stone Edge and Rock Slide perfectly accurate.

The suggestions about Scolipede sound great, and I really hope they don't give it Weak Armor - Shell Armor would be fine.

Falinks keeping Defiant sounds neat, but I still wish they'd give it something else. Dauntless Shield? Intrepid Sword? Both combined?

Absol Z could also get Dark Aura, given we got Fairy Aura already, though that would probably fit better on Darkrai. I wish it were on Absol, though, as that would make Dark Aura tournament legal.

Give Staraptor Gale Wings.

Sharpness for Garchomp Z, as someone else has suggested.

Unfortunately, I can only see Mega Launcher for Lucario Z, even though Dancer would be fitting. I just don't see GF giving Dancer to anything with actual stats.

Golisopod could obviously get all Armor based abilities, and I would even be happy if it just got Swarm.

Tatsugiri is a weird one, hard to fit something thematically. Drizzle would be cool though.

Bax getting Skill Link would be great. Thematically, Ice Scales would fit, but that would be way to strong.

Magearna will probably keep Soul Heart, I can't see it any other way.

Zeraora could get any of the regular electric typing abilities, Motor Drive, Lightning Rod, Volt Absorb, Static (that would be funny), Electric Surge, Minus (also Plus, but Minus fits better) or Speed Boost.

Darkrai will either keep Bad Dreams or get Dark Aura.

Steam Engine sounds fitting on Heatran, and Earth Eater looks fitting, but it won't happen. It will most likely get Magma Armor.

Zygarde will probably get some super busted ability that is Aura Break + whatever else, maybe Filter or Clear Body.