Black Knight wouldn't fit due to the nature of the Ebony Blade. The more you kill, the more mad it drives you.

Again they are setting up an Blade and Black Knight Partnership in the MCU, as long as Blade is there, Black Knight isn't fall behind. Also, he could use another weapon besides the Ebony Blade, He doesn't always have to use the sword lol.

From what I have heard, Doctor Strange 3 won't involve the Midnight Sons anyway.

@IronWidowMaikuB But is the Black Knight a killing hero?

Again it doesn't matter if they are setting it up which they are as seen in Eternals and Black Knight don't have to kill their Enemies you know lol. He could Easily take them out and let either Blade or one of his other teammates finish the job.

But would he let that happen? Is it his personality?

What is he going to do Not fight lol? Just sit around holding onto the sword and do nothing but sucks his thumb. If 616 Black Knight Can be a Avenger who I'm pretty sure have killed in their day then I'm sure 199999 Dane can fight as a Midnight Sun.

He could fight without killing. But if the Avengers casually killed, Hulk wouldn't be telling the Avengers 'aye, this aint us'.

Again you're missing the point of the fact that 616 Avengers have killed and two of their main members are Clint Barton who was Ronin and no matter in what universe have enough bloodshed to kill off a entire Army and Natasha Romanoff who's killed just about two armies and that's not getting into what Thor and Steve Rogers have done and 616 Dane spend most of 1990's working as a Avenger and was pretty close to 616 Nat. They are setting up Dane working with Blade and If Blade is apart of the Midnight Suns then Dane is too.

Not to mention in terms of the mystical lineup we have so far, all the personalities of the Moon Knight system have killed in some way, Elsa Bloodstone and Jack are hunters, (in one way or another) and Blade has sorta killed people. If you consider vampires that. And Ted has killed people with his toxic hugs. So yeah, the team are not exactly going to be judging each other on their murder count.

Not to mention this is a different version. Dane was set up more as a kindhearted teacher before picking up the Ebony Blade.