I would never consider printing on fabric with a laser printer--I work in technology and have had several of different brands over the years, both home and high-end level.
Even if the toner (laser printers don't use ink) is colorfast, I would be worried 1) about getting lint in my expensive equipment, and 2) about burning the fabric--laser printers run hot, and color lasers even hotter. Plus, they are considerably more limited in the type of media they will accept and function with. And if you have a warranty, I'm sure attempting to print on fabric will violate it.
Compared to buying a new printer, paying $18/yard at spoonflower.com or another POD fabric place seems downright cheap!
I wish it were realistically possible, though... toner is so much cheaper than archival fabric ink jet ink! :)