I think it's more likely that Ralsei isn't Asriel, but there's still an off chance Asriel and Ralsei are connected somehow. I think if Asriel IS Ralsei that at this point that would be... more of a twist, because it's one of those things where Asriel = Ralsei is so obvious as a conclusion most fandom would be like 'uh no'. I think if we believe Ralsei is Asriel, well... we know Asriel likes making games these days so. That's the one thing I can go 'maybe' about. Even if Asriel was Ralsei, I think Ralsei would be more like a character Asriel played than 'actually' Asriel or reflecting anything like his sincere thoughts.

I think most signs in the game point to Ralsei being something else though. I know the headband theory is common, and I'm inclined to agree that Ralsei represents the toy headband. I think he shares a similar role to OG game Asriel (a prince) and I can see vestiges of Flowey in him - I always think Ralsei is probably something similar to Flowey's first runs where he tried to make everyone happy, that we didn't get to see. But I don't think he's -actually- Asriel. We know 'being bad at naming things' is a family trait, so I think actually Kris naming Ralsei is something they did that just cements them as sharing this family trait. Or arguably maybe Asriel was involved in the naming process for Kris' monster OC version self. We know he can't name shit. I think Ralsei also tends to represent this fanon 'nicer' version of Asriel that most fans have conceptualized Asriel as being. So shifting this into the audience's mind and having it front and centre is going to a dramatic counter to what we see of Actual Asriel in canon... imo