Like the title says, for about a month now BO4 PC matchmaking has been broken, no one is able to find any MP/Blackout games (or even another single person in a lobby) in any region for any mode (several reddit threads about it). You are not able to play at all. Activision acknowledged the issue and gave the standard "we'll look into it" and hasn't got back to anyone, and we're not hopeful because only maybe 100 of us still played it. Prior to this, they also completely deactivated SEA servers without telling anyone, so SEA users had to play with high ping on NA servers until this happened.
On top of this, there has been a bug in the Black Market for 2.5 months now where just entering it will crash your entire game. Again, Activision was notified, "we'll look into it", no info or fixes since then. So when matchmaking WAS still working, you couldn't even use the supply crates you earned to unlock new stuff.
I know you said you didn't want to do BO3 because you feel you couldn't add anything to it and it still has a fairly thriving PC community (even with all the hackers), but BO4 is a different story. Only a handful players, which makes it even more frustrating when there is a hacker in the lobby, and now PC matchmaking is officially dead.
I, and several others, would love if you could make a Plutonium for BO4 and implement your anti-cheat tools for it, for both MP and Blackout.
If you also feel like you could not add anything to BO4, I have played for a while and could offer feedback on aspects that could be tweaked to make it less frustrating for people to play that would fix a majority of the criticisms players have of BO4 MP that make them view it as one of the lower ranked CODs.
Some easy ones would obviously be nerfing what the entire community generally agrees are overtuned weapons (to the point where game chat is flooded with both teammates and enemies trashing the player using it) like the VMP, Crossbow, etc.
You could also completely remove Jungle Flooded from the map rotation, which most of the community hates and half the lobby leaves if it pops up due to its overuse of the swim mechanic.
You could fix how certain ai killstreaks, like the snipers nest, stay on the map far too long and are far too effective for the minimal amount of kills needed to get it, and also often causes people on the enemy team to leave once they are called in, because snipers nest easily snowballs into all the other higher ranked ai scorestreaks with the player hardly having to do anything.
You could fix the duration, ammo count, and effectiveness of some of the specialist tacticals and special abilities to make them more balanced and offer proper risk to reward.
One of the players also hosts a dedicated Blackout server where we have custom Blackout games once a week (maybe only 6 players ever join), and made a tool that allows you to add bots to Blackout. That could be implemented as well to back-fill lobbies until the player count is reached, similar to how COD Mobile does it.
I just offered a general overview, but I've thought about these a good bit and would be more than happy to offer specifics for everything.
BO4 was the last "true" arcadey run-and-gun/boots-on-the-ground COD before all the changes implemented in MW2019 moving forwards, and before Activision moved to their new engine that replaced SBMM with EOMM which made everyone's play experience worse (Westlayne has a good video of EOMM on Youtube if you don't know what it is.)
And not to mention Blackout is infinitely better than Warzone
Please, save BO4. I would love to go more in depth with you on changes you could make if you take up the project.