Why would any RM want to attend a freshman Book of Mormon class? Segregation in Book of Mormon classes is not only good, it’s essential. If you mix the freshmen classes with the RMs, you’ll get RMs who are frustrated by the lack of understanding among their classmates and rudamentary lessons, or freshmen who are frustrated by conversations that are too in-depth for their understanding.
Returned missionaries have (or at least should have) distinct advantages over non-returned missionaries: They’ve been through the temple and have a greater understanding of the principles of the gospel, they’ve been teaching from the Book of Mormon for at least a year and a half (mostly two years) and they’ve had a personal study time set aside every day where they’ve had an added blessing of the Spirit to guide them in those studies.
Now again, why should the two be mixed? I don’t know of any good reason. Thinking back on my EFY-like experience in my Book of Mormon classes, I sometimes wish that I’d been able to attend an RM class. If I had, though, I’m sure that I’d have been far behind in understanding.