One of the most contentious aspects of 2008's Mortal Kombat vs. DC Universe was the fact that it wasn't R-rated. Back then, DC couldn't fathom having heroes and villains maiming in the manner Mortal Kombat fans loved since the '90s. Thus, while Midway Games did do a decent job of making this one vs. one fighting game, it felt diluted as it didn't stick to the violent potential the crossover offered.
However, before Midway went bankrupt in 2009, the franchise was sold to Warner Bros. Interactive Entertainment, which has worked wonders since, with NetherRealm Studios putting out games in the Batman: ArkhamVerse, as well as the new MK games and the Injustice series. Interestingly, given the change in climate at DC and how iconic characters are now able to cut loose more, now's the perfect time for an MK vs. DC sequel to take place, but in an R-rated setting.
DC Finally Allows Blood & Gore
The perfect template for this sequel lies with the Joker, who was a DLC character in Mortal Kombat 11. He was using crowbars, knives, guns, and bombs to decimate opponents. He even had his jack-in-the-box weaponized and had acid flowers as well as a Batman doll, proving DC wasn't taking things too seriously in terms of restrictions. Joker was allowed to be his bloody self -- something not even the movies, games, and TV shows allowed.
MK vs. DC II can stick to this aura, bringing back Deathstroke from the first game but with guns, swords, and bombs that allow him to skewer opponents. This aesthetic fits fellow assassins such as Lady Shiva, terrorists such as Anarky, and villains like Harley Quinn and Punchline. It even syncs up with vigilantes who cross the line such as Red Hood, the unhinged Arsenal (Roy Harper, the ex-Red Arrow) with his arm cannon, and Azrael.
The point is, all these DC characters have powerful tools that'd make for squeamish Brutalities and Fatalities, with this game not censoring them how the books would. With the show Peacemaker being curated for adults, following up on the glorious kills from James Gunn's Suicide Squad, Warner Bros. is clearly allowing darker paths to be taken. Such a direction enables these seedy characters to be truly unleashed against MK's most elite killers.
MK vs. DC II Doesn't Need Heroes
Admittedly, Warner Bros. treads lightly on putting heroes in these situations. The fact that the Injustice comics had Superman punching through Joker, yet the game didn't honor this aggression, spoke volumes about how DC viewed Kal-El, Batman, Wonder Woman, etc. murdering people. However, this has changed in stories such as DCeased and DC vs. Vampires, which see more gore. Still, a sequel doesn't need these heroes as it can simply take place in a different reality. Or, it can take place in a pocket dimension where overlords like the MK11 Joker, Shang Tsung, Shinnok, or the Elder Gods see who are the most brutal fighters to form a legion and conquer the Multiverse.
This can revive Dark Khan (the amalgam of Shao Kahn and Darkseid) from the first game, with vicious MK figures such as Onaga (the Dragon King), Blaze (the fire god), Scorpion, Baraka, Mileena, Ferra-Torr, Kano, and Skarlet deemed worthy to take on the DC tribe. DC can bring in new tyrants such as Deadshot, the back-breaking Bane, Lobo with his bike, Peacemaker with his destructive helmets and guns, and even Doomsday. Warped versions of heroes can work as well, such as the Injustice Superman, Reverse Flash, Batman 666, or the Flashpoint Batman.
Simply put, there are enough iconic warriors on either side to be considered dirty enough for a battle royale to the death. Such figures make the narrative of gladiators willing to kill much more believable. DLC packs can add them intermittently and build buzz in marketing, especially as there are a ton of niche characters to use at a time when both properties are quite popular. Ultimately, there's no better time than now, especially in a Gunn-led era, as he's someone who knows to not fight the nature of these combatants.