Slashing Molly would take an equally unique woman to pair her with, and I haven't seen anyone that she could get that close to in canon at all.
Were I to slash her, it would be with a "the witch next door" type of character, and she does not strike me as the sort who has made any strong female friends on a personal level, or any strong friends on a personal level, for that matter. She strikes me as too devoted to her family to put much time and interest into anything outside of it; Order of the Phoenix is serving her family by getting rid of Voldemort to make it safe for her family.
If I knew more about her past, she might be slashable as a schoolgirl, but not after she got seriously involved with Arthur.
If she were to be involved in any romance after she got together with Arthur, I could only see it in foursomes -- her and Arthur meeting up with another like-minded wizarding couple for some fun. And I don't see anyone like that in canon either.
Then, I just realized that I see the Weasleys as an outsider might view a Heinlein Family: redheaded, smart, et cetera, keeping fairly low to the ground. Only a Heinlein family would be more unrealistically perky, and the Mater would not be worrying about cash so much and the Pater would be more popular at work.
(And if they were a Heinlein family)
'cept Molly would have to be bisexual, then, and so would Ginny, and Weasleycest would be totally canon, or at least Weasleycestuous!UST. Though probably not so much between the boys.
And the elder Weasley boys will come home with lovely brilliant redheaded brides. And there will be multitudes of cats, and everyone will start reading Kipling, Mark Twain, and the rest of the Muggle Classics, because they were written by wizards and they got leaked to the Muggle community.