Characters Better Suited For Tycho's Chair in "Poker Night at the Inventory"
Regardless of your opinions of Penny Arcade, Tycho just isn't a good fit: He's the only character who isn't actually a video game character (besides that brief stint in those Rain Slick games, which was mostly just a physical resemblance IIRC); He's the only character that swears copiously, requiring a higher age limit and an added option to bleep his statements; And, (like the Heavy admittedly) he seems like a ringer to gain fans from a heavily-established outside fan-base.
These aren't just alternates for the sake of alternates. I'll clarify why they're a better fit, but overall they need: An existing voice actor, an existing 3D polygon model and the capacity for quirky and amusing dialogue (for both comments when playing and conversations with the others). So Gordon Freeman, for example, would fail two of those requirements with his mute nature.
Very much a "closing the gate after the horse has bolted" list, but it's fun to dream.