A bit late since the news about the blizz-coop community collab broke out but I wanted to share some things that would make help make some units or prestige be more easier or better to use and some reasoning behind the changes.
Raynor:
P3 - Mule Repair rate increased by 1.5-2x; I find that healing up 700 HP BCs is both expensive and slow but I would rather make it just expensive.
Artanis
P2 - Reduce/Remove the energy cost of Project Power Field, Increase the AoE by 10-20%, and in exchange increase the cooldown to 5-10 s; I think this should be a fair trade in exchange for maximizing the army teleports while it not being as taxing to energy costs the increased area also helps in the late game when a massive army can barely fit in it.
Kerrigan:
P1: Add Detector to either Creep Tumors or Kerrigan herself (albeit with an upgrade); I think the loss of worms in exchange for creep on steroids is not a fair trade and microing overseers when your core army is hydralisks is a pain to manage against air comps as they get shredded without any mutalisks to take the heat.
Swann:
P3 - Reduce the CD nerf on top bar abilities; P3 is fun but hard to use and support in Brutal where not having a calldown to eliminate or chunk down an attack wave could result in massive losses. I think this should make things a bit more fair.
Zagara:
P3 - Have Frenzy work on own units but not on ally units or Increase the duration of Summoned units; let’s face it P3 Zagara isn’t P3 Zeratul, P2 Kerrigan, or P2 Tychus and still needs an army to support her come mid-late game.
Vorazun:
Void Rays - Add the prismatic alignment ability; Co-op battles are mainly decided in a few seconds and that means void rays don’t have the time to wind up to their full power in that span of time. Allowing them to instantly power up on critical battles like hybrid waves would increase their viability.
Karax:
P2 - Allow to build cannons but at increased cost; P2 is my favorite but it feels like you’re letting your ally down on defensive maps like DoN or TotP, I think having access to cannons even if at say 200-250 minerals is a good price to pay for at least having the option of static defenses, hell they can even increase the price of shield batteries too and I think that’s still fair.
Fenix:
P2 - Remove the HP/Shield nerf on Conservators and make them full price; As much fun as P2 is in running a protoss Tychus, I feel that conservators get focused and die too fast which leads to more champion deaths.
Horners:
Widow Mine - Further increase the range buff of sentinel missiles from black market launchers upgrade (say 10 range); I think widow mines still die too fast and aren’t a good stand in for a base defense.
*Nice to Have - After upgrades, allow widow mines to fire while unburrowed but at a further increased cooldown; this essentially turns them into mini Zeratul Abrogators and allows them to be able to be used in assaults without the hassle.
Abathur:
P3 - Remove/Reduce nerf to Biomass needed for UE but scale the weakened effects of biomass to compensate; P3 is just so hard to run early game because of the increased biomass requirements, I feel this would help the prestige get up and running faster.
Dehaka:
P3 - Dehaka and Zweihaka share experience but increase leveling XP to 15 by 25-50%; I think what puts me off of P3 the most is that you have to gather experience individually, I think the mutual death is already a fair trade-off without you micromanaging who gets to level up first.
Honorable Mention: Stukov P2 - Needs to be reworked; I didn’t include it since I think P2 is far from redemption with just some number tweaks, the change is relatively minor and honestly not worth the reduced infested duration. I think they need to rework it to be like its namesake and maybe work on the plagued munitions upgrade mechanic.
Feel free to post what you want to see change in coop if they do ever decide to make changes other than some bug fixes.
