The issue with the EX cards we have is that they are basic but many have 170-180 HP. A stage 2 one would probably have a ridiculous amount of HP. Do we really want multiple Pokemon with HP as high or higher than the old Wailord ex from Sandstorm(or the BW5 one as I think that has 200 HP too)?
I'd rather have Charizard and Blastoise as non-EX cards. I do have to wonder one thing: why release Charizard and Blastoise together but release Venusaur earlier?
EDIT: Now that I think about it, I'm pretty sure we would already know if Stage 1/2 EX cards would be in this.