I think they already crossed that line with Mahalia Jackson, and Billie Holiday, and Bessie Smith, and Etta James.
And Johnny Cash!
Others for consideration:
Roberta Flack
Yvonne Elliman
Wendy O Williams
Charline Arthur
Francoise Hardy
The Rock & Roll Hall of Fame is the biggest joke this side of the 2016 Republican Presidential primary candidate field. Cheep Trick and Grand Master Flash are in, Moody Blues and Yes are not? One hit wonder, Joan Jett; and the Staples Singers are in. But Joan Baez and Carly Simon are not?
Another worthy woman, if only for having the best rock female voice of all time would be Annie Haslam of Renaissance.
Joni Mitchell was a Rock musician?
In the “Completely Deserves Inclusion But Will Never Even Be Included In The Conversation” category, Ani DiFranco.
Maybelle Carter.
She gets her due from the country end of the spectrum, but she deserves recognition for being crucial to the development of rock music too. Folk music was just as important to the genesis of rock music as the blues.
Suzi Quatro
Okay, I figure country from Nashville and blues from the delta met up in Memphis/Jackson to become Rockabilly
The Carter Family were proto-country. Country, like rock, didn’t exist until much later. The Carter Family were folk, and folk music led to the folk revival, which was where people like Bob Dylan and Joan Baez came from, along with the Byrds and all those West Coast psychedelic bands.
Folk music is kind of written out of the history of rock because people seem to prefer the the idea that rock music was simply white people copying black music. The truth is a lot more complicated, with American blacks and whites musically influencing each other back and forth for generations before distinctly American forms like jazz and blues and bluegrass started emerging.
Spoken like a true Australian! 
Seriously, America has a pretty distorted lens, or set of lenses, when it comes to viewing this stuff. If any aspect of the U.S. can truly be described as a melting pot, it’s our music.
Joan Jett is much more than a one hit wonder.
Memphis Minnie - oh hell yeah.
And Francoise Hardy carbonates my hormones. That is all.
Tori Amos
Hell, Alanis Morrisette qualifies this year. 25 years since the release of her first album came out in 1991.
Kim Gordon of Sonic Youth?
Isn’t everybody in the Rock HoF?
I understand that Gustav Mahler is in consideration this year, because he used to yell “Turn it UP…play fuckin’ LOUD!!!” at the Vienna Philharmonic.
“This viola goes up to eleven.”
I can’t believe Joan Jett and her one hit wonder cover version is in, and these are not
Chrissy Hind
Pretenders - Precious - YouTube
Big Mama Thornton - if you don’t know who she is look her up. I find it utterly incredible that she isn’t on this list, being as the played a major part in the emergence of rock n roll- YouTube
Sylvia Robinson, she may have had more influence on current music than anyone still alive, I doubt the rock n roll hall lot would appreciate it though - some of you might even know why
Connie Francis - probably not know for rock and roll, but she did a few well known numbers.- YouTube
Connie Francis – “I’m Gonna Be Warm This Winter” [US 45] (MGM) 1962 - YouTube - you might know the Gabriel Cilmi version
Terri Nunn of Berlin, you’d think she would be in there - given some of the other names
Grace Jones - If you are gonna include Donna Summer then surely Grace would be listed - lets face neither of them would be considered to be rock - equally you would not list one above the other
Sister Rosetta Tharpe - No-one can ignore her contribution to rock- YouTube
Annie Lennox - A little surprised she isn’t included
Joan Armatrading
Joan Armatrading Drop The Pilot - YouTubeEhh, curing the sexism inherent in the system isn’t going to do much toward fixing the RRHoF. It’s problems run deep. I blame the parents.
Hate to break up a well sourced rant, but The Pretenders are in the class of 2005.
And Joan Jett is NOT a one-hit wonder.
This argument is already over. Madonna is in, as are Donna Summer (and James Taylor, already mentioned.) Lots of rap artists are inducted. It was decided many years ago that “rock and roll” included “and the forms of popular music it has inspired.” That is the standard.
I am gobsmacked Annie Lennox isn’t in.
I’m 55 and there are no women of my generation in there (yet); Madonna comes the closest, I suppose. I’d like to see Natalie Merchant, Liz Phair and Michelle Shocked considered.
Yeah, seriously, how the fuck is Annie Lennox not in there?