I doubt it will fail. And here's why: I don't think the base is as "divided" as some people think.
The theory is that the fan base is split into three groups: a large group of 4E players, a large group of 3.X/Pathfinder players, and a somewhat smaller group of earlier-edition players. But we are all tabletop RPG players, and there is a lot of overlap in our materials. A lot of people who play one edition also buy and adapt material from other editions to use in their game.
So as long as WotC focuses on QUALITY OF PRODUCT, they cannot fail. As long as the books are well-written, with imaginative adventures, clear rules, and quality artwork...we will buy them. We might buy them them because we are curious, we might buy them because we are switching to the new 5E, we might buy them to adapt them to our older system of choice...but if the quality is there, we will buy it.