Yeah, that's my read. It never drops below 50%. I'm guessing it starts there, too. The whole system is based on putting that together with the Galaxy at War score, so a 5000 GaW score X .5 Readiness = 2500 GaW score. Who knows what that'll mean, or if you'll actually get a meter showing that, or what.
Also, some single-player demo thoughts:
-Love that they've rethought the difficulty levels. In ME2, every enemy on Hardcore/Insanity had some sort of armor/shield/barrier, even the basic grunt-level enemies like LOKI mechs or husks. In ME3, the enemies have the same defense profile regardless of the difficulty--they just do more damage/attack more aggressively on higher levels. Given that biotics like Pull and Singularity didn't work on shielded/armored enemies, this seems like a good way of keeping the way you use classes consistent across all levels, rather than broken.
-The ability to customize your loadout and have that affect cooldown times is really cool. Playing a caster carrying just a pistol or SMG is awesome, because an adept can throw out singularities/warps every couple seconds, and an engineer can do the same with incinerate/cryo. Lightly-equipped adepts being able to do their own warp explosion combos is going to be great. I even like that it allows for unorthodox combos, like a CQC infiltrator that carries just a shotgun. Way cool.
