Maybe. Main reason are probably animations, because from what we know both forms will be usable in combat. Strange they didn't go lazy way: give visage to all races + make dragon as only combat form. That would shut up every discussion of making new races for Evoker or new classes for Dracthyr.
And next Legion info came 3 months later. And Legion reveal didn't have massive interview campaign that revealed new stuff never talked about in reveal. And usual week-to-week info was more sparse than now (just check wowhead, it was mostly 6.2.2 info from time to time). And Alpha started even after Blizzcon with just Demon Hunter zone, before end of year we didn't even have half specs available. But no, we don't have arguments.
Fastest reveal->launch I remember was BfA, even there Alpha took 3 months to launch. 3 months after DF reveal is mid-July, which sounds like reasonable date for Alpha, especially since 9.2.5 launched faster than many people expected. We will see.