I think a lot depends on how different 1.5 is, and whether it's another big departure like 1.4 was, minimally modified, or a partial return to 1.3. I'd put my money on another big departure. With mixed reactions to 1.4, I don't think they'll tweak the recipe slightly, and if they were going to return to a formula more like 1.3 I think they would have already done so.
I've only had 1.0, 1.3, and 1.4, and to me 1.0 and 1.3 were minimally different from a taste and texture standpoint.
Some people love 1.4. If it disappears and some of those people don't like 1.5, I think you'll see inflated prices for the remaining 1.4.