The problem is that a lot of the publishers use Diamond even for their bookstore trade distribution. DC and Marvel have only switched within the last 5-10 years. The interruption in cash flow from monthlies and the need to spend more upfront at the same time would probably put just about everyone but the Big 2 (and possibly Top Shelf due to it already being their model) under.
That doesn’t even take into account the devastation it would cause in the LCS market. The vast majority (if not all) would probably cease to exist overnight.
Meanwhile, Marvel continues their 99¢ day and date trade sales. The only one I was interested in is X-Men: Grand Design which I will probably buy anyway due to the oversized format. Maybe that’s the future, making print something special separate from digital.