Will he be the first person to have two separate roles in the MCU (apart from whatever Stan Lee was)?
He will not be the first. Here is a good run down. Ironically, Ali isn’t even the first Luke Cage villain to get a second role. Alfre Woodard played the grieving mother who convinced Tony to kick off the events of Civil War.
Gemma Chan was arguably highest profile in terms of plot importance if you don’t count Agents of Shield and the Netflix shows… She played a named bad guy in Captain Marvel, then Sersi in Eternals. You’ve also Michelle Yeoh who played a Ravager in Guardians 2, and Shang Chi’s aunt. A bunch more had voice/CGI roles for their second appearance, like Linda Cardellini or Benedict Cumberbatch.
No, it looks like it’s pretty common for marvel to reuse actors, actually. I had no idea until you asked though, and there’s even another actor from Luke Cage with multiple roles coincidentally:
