Its been no secret that DC has decided to keep their movie and TV universes separate. Fans know and understand this fact, but the unfortunate byproduct is that some characters become off-limits to the TV universe when the Movie universe is planning (or already is) using said character. We have seen this with the obvious absence of Batman and Superman, but when Arrow removed Deadshot, and now Amanda Waller, fans took notice.
Now a new rumor has emerged that this is the reason we haven't seen Deathstroke since his brief cameo (following his major Season 2 arc) in Season 3.
Recently on Marc Guggenheim's (Writer, producer, and creator for Arrow, The Flash, and Legends Of Tomorrow) tumblr, a fan asked the following question:
gintoki79 asked:
You said that only Deadshot was off-limits, and Amanda Waller & Deathstroke are safe. But you guys killed Waller off just like that, and she doesn't seem like she will ever return(Because bullet to head). Who's next to be killed off? Katana? Once Deathstroke arrives in the DC movie, will he be also killed off too? This is really frustrating, that all awesome characters are being written off, because of the Suicide Squad movie, and is a slap to the face of Arrow fans.
Marc Guggenheim:
Um… I never said that.
But another fan question seemingly sealed the deal.
greenarrow-bbb asked:
Any possible chance of either Slade or Walter returning throughout the rest of Season 4? #Arrow
Marc Guggenheim:
The character of Slade Wilson is currently tied up in another DC project. Walter is more likely.
Now reddit has run rampant citing this (among other things) as definite proof that 'Arrow' is no longer allowed to use this character because of an upcoming inclusion in the DC cinematic universe.
In the past rumors have circulated that DC has Deathstroke playing a secret key role in the upcoming Suicide Squad, and other rumors have indicated that the character was poised to be the primary antagonist of the now failed TNT Teen Titans TV Series.
While no actual confirmation has been made to where the character currently stands, one thing is clear, DC's TV Universe can no longer use him because he is being used elsewhere.