Why not?showing your prospective customers works-in-progress of the upcoming "edition", NO.
I think it suits Wotc's current business pretty well. They have invested in establishing a market relationship of feeding the D&D product to buyers through on-going subscriptions and on-going events. So, tieing marketing on this on-going engagement with the public -even the push towards a new edition, the making of it and its eventual launch- is pretty much a given. So far, playtests, arcana uneathed alternative rules, all to be shared with the public. They even try to show to their public that their skepticism, their critical thoughts, their own criticisms regarding the products of D&D they make and sell are shared with them in this Legends & Lore column. Along with the solutions, the new directions and developments everyone desires (players + developers of D&D).
So, how would you market 5e?