Clearly novels have gone through fat and thin phases over time. I'm told that in post-war period, the shortness of many novels had a lot to do with the increasing cost of paper (or tired writers; from 1920 right up to the advent of metrification, we had to measure out our lives in coffee spoons.) Generally though, writing doesn't seem much dependent on the medium. As far as I can tell from exhaustive searches at the great libraries of the world, paper had long existed before the word 'platform' existed to describe what words take shape on. I've come to think that aesthetics matter not a jot beyond the first few pages and the only real constraint is practicality. So yes, a novel can be written on a roll of wrapping paper, index cards, a laptop, a smartphone, a typewriter, a dictaphone, post it notes, the walls of your padded cell, ansaphone machines, till receipts, bank statements, a source code editor, your blog, backs of envelopes, napkins, the palms of your hands, tapestries , and via word processors, text messages, emails, scrabble letters, pictures, your own blood, someone else's blood, or sweat and tears (not so effective), tattoos, Facebook updates, pen, pencil, crayon, knitting needles, piped icing sugar, graffiti, or your grave. John Keats even writ his name on water, though that may not work for us.