I wouldn't be suprised if they made episode 3, then made a full-fledged HL3 (or should that be HL4... nah), followed by maybe some HL3: ep's. During the space between ep 3 and HL3 they'd probably have an expansion like Blue Shift and Opposing Force were.
Oh man. You just like... wow. You blew my mind.
I mean, Valve has been hinting at Alyx getting a sex-change for a while, but I never thought about... wow.
Arctic Headcrab/Zombie would be cool, considering Headcrabs CAN adapt to their environments (Poison & Fast). I'd expect they white and furry.
A Behemoth-sized synth would be pretty cool for a one-off encounter, possibly fighting it in a 'Shadow Of The Collosus' style.
I'm also in favour...