Bad idea, consumer confusion. Nintendo tried this with the Wii U. Granted that wasn't the only reason the Wii U flopped.
I don't think having two models with different hard drives is a problem or confusing at all. Consumers are used to this, they buy phones after all. The 360 and PS3 both launched with multiple storage options and I don't think people found it confusing.
But this is about a "pro" console, not just a storage upgrade like the WiiU.