I think having Muppet characters that are based on actual races defeats the purpose of having Muppet characters. Sesame Street has always been diverse with its human cast. It's imp[ortant for a show like Sesame Street to have a truly diverse human cast so that kids can see all kinds of people interacting. A kid in NYC will be used to diversity, but a child in the middle of Nebraska may not be.
However... The Muppet characters are supposed to be relatable to everyone, regardless of race. That is the point of having monsters and "Anything Muppets". Instead of focusing on specific racial issues, you can tell an allegory through Muppets which is far easier for a child to understand. You can tell a story about prejudice without singling out a specific race as the victim or the perpetrator. You can show cultural diversity the way Sesame Street always has, by showing real people in real settings. Having Muppets that are specifically identified as different races defeats the purpose of having Muppets on Sesame Street to begin with and runs the risk of inadvertently alienating some groups. The Muppets on Sesame Street shouldn't be black, white, Asian, etc.