Yes, Mr. Gib... I looked at that too, and from the side looking at the derailleur stops I would agree that it's not possible. But it also depends on both the curvature of the tube and where exactly they end up crossing so, although I suspect you're right that it wouldn't work, it'd be worth a shot. The pic below is what got me to thinking that if the crossing point, which is well below the half way point of the downtube is below the plane of the downtube then it could work. You don't need much clearance, even a millimeter will do... a side on shot of the downtube and cables at that point and you'd be able to tell for sure.
Also agree that on modern bikes where the cables enter the upper half of the downtube (which is massive these days) there is no real reason not to cross them internally as it provides for a much more relaxed cable housing curvature which helps shifting. Wherever possible I will choose this type of routing. It seems to have been often forgotten about these days, but really should be resurrected again in light of fat tubes, internal routing and entry points of cables. And you're mostl likely right about your EP not being able to use this routing either. It's similar to my C50, not possible.
_________________Colnago C60 - PR99
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Trek Emonda SL Campagnolo SR; Trek Koppenberg - Where Emonda and Domane Meet