Snyder has mentioned before that the Robin who was murdered by Joker is intended to be Dick Grayson, which really bucks fan expectations. Traditionally, and famously, the Robin that Joker kills is the second person to take on the role, Jason Todd. Grayson is well known for eventually stepping away from Batman and becoming his own hero, Nightwing.
Speaking to TheFilmJunkee, Zack Snyder discussed an “Easter egg” that pertains to Robin in his upcoming cut of Justice League:
There’s a Robin line, like… There’s a Robin Easter Egg in Justice League… That I think you’ll have to wait and see, I can’t say exactly.
Snyder also offered the following on the topic of Robin actually being a featured role in a future DC film:
Would there be a plan to have more Robin? In future… In whatever future story? There would be.
He also detailed a potential flashback that could bring the character into the fold while also explaining his absence:
I mean to me, the way you do a Robin story in the Justice League universe with Batman is like, drinking and remembering… and we see what happened. We understand who Robin was to him and we get to experience what was the circumstances for the Joker and Robin coming together.
Regardless, ever since that shot of Robin’s abandoned suit in BVS, fans have been quite curious to see how it all went down. It’s been long speculated that the reason all of the Joker’s teeth are capped in Suicide Squad is because Batman knocked them all out after the Clown Prince of Crime took Robin’s life.