I think the catalyst (for consoles at least) will be how awful sales appear to be in NPD threads for certain titles despite their being a relative success. For example, we have reports that about 70% of Driveclub sales have been digital (It was some reliable report, at least, I think?). It will look like it completely bombed in the October NPD results which is horrible PR and optics. Same deal in every country that doesn't track digital. You can surely agree that that one talking point alone will cause massive console warring here. I sort of get the vibe that Forza Horizon 2 might pan out the same way though of course I have no scientific evidence.
Sony and Microsoft will eventually feel compelled to release digital data in order to save face. As pre-loading becomes more popular and bonuses are actually starting to be offered for digital pre-orders this will slowly add up for the big publishers, too. Imagine a point where 25-50% of something like a Madden, FIFA or CoD were digital. On just physical units that would look like a catastrophic year-over-year decline--every year--where perhaps total sales could be up. For the same PR reasons the Big Guys will eventually have to play along, too.