I'm a big fan of Bonnie Langford but I don't think she has what it takes as an actress to take over an iconic tv role and make it her own. Develop a new character that may possibly become iconic in time, yes, but taking over an established role... I think that needed an actress of the calibre of Jenna Russell to take on Michelle.
(And, yes, I know Bonnie has played many characters on stage, some of them iconic, but the difference is that stage roles are played by many actors, all putting their own take on them, and audiences expect stage actors to do that. Michelle, on the other hand, had only previously been played by one actress, and most people who recall the character have a fondness for her, so stepping into that role was a far harder and more difficult prospect.)
I wonder what Sue Tully thinks of the recast? It would be nice if she were to speak up in support of it.