When I first read that, I will admit, I got worried. But then I thought it through, and it's not so bad. I'm assuming (probably wrong, but never mind) that Mariah's up for Adelaide. If so, she should be OK, because all she really needs to do is belt out 'Adelaide's Lament', 'Bushel & a Peck', 'Take Back Your Mink' and 'Sue Me'. There's not a great deal of acting necessary other than being pissed off at Nathan. If she's being suggested as Sarah, however, we may have a problem. I just don't think she's up to the part. Fair enough, it's not intense Shakespeare or anthing, but it still requires some work.
She also doesn't strike me as capable of acting drunk whilst singing ('If I Were A Bell') without it looking totally stupid. She'd probably take the root of going out of control from alcohol, when it needs to be more that it's given her the courage to do what she's wanted to but been too afraid. But at least it's not Madonna, who I heard was suggested for Adelaide at one stage. And I agree, Nathan Lane must be Nathan Detroit. (Sorry for ranting for ages, but I have strong feelings about this. Problem is, they do tend to produce random streams of thought like this.)