I think the Swift is one of the best foot-launchable aircraft around and pretty much at the limit of what we can do with current technology. If you want to do a lot better, you need a smaller and lighter wing. The only way I can think of this, while keeping a slow enough stall speed for foot launching is to incorporate a cloth flap. Not the normal flap-like thingy, but massive sails that double or triple your wing area for T/O/landing, so you resemble a bat. Sails can be rolled up to the wing/fuselage. Another approach is to make hollow ribs, much larger than your wing and slide them outwards during T/O, landing, while being covered with cloth. In cruise you will have a tiny wing and a lot of cloth, folded up in your fuselage. At landing/TO you can winch the ribs until they're spread over your wing and you have something that looks like a deltaflyer.