We have 2 older style Classic Birdies and one Monocoque.
I see the following differences between our Classics and the World frames.
Front suspension pivot change (like monocoque) simplifies mounting of mudguards (fenders)
More tire clearance at top of front swing arm (The older classics have a mounting point for caliper (road bike) brakes which reduced tire clearance)
Newer headpost clamp (looks like monocoque one)
Cable routing runs through top tube (like monocoque) which is a bit tidier
Top tube changed from oval to modified triangular. May reduce folded size a bit? May reduce frame resonance?
Seatpost clamp style improved. Worthwhile but may increase folded size a fraction
New style seatpost (like Monocoque) provides more front back adjustment
Has mounting points for rear and front racks (like Monocoque)
I'm not sure if the seatpost angle is the same as the Classic, more upright like the Monocoque, or something different

Anyone got anything to add?