I always thought the P-39 was an interesting layout, and the more I read about it, the more I become convinced that it's lacklustre reputation is partly myth, partly bad luck and partly due to features other than the mid-mounted engine. Just a few things:
1. The mid-mounted engine forced a relatively long length or fuselage to be rigid, with some weight penalty. However Bell made this much worse by adopting the car-door layout, which denied them the use of the full fuselage depth for strength, thereby forcing the shallow "canoe" underneath it to be heavily reinforced.
2. Adding to the weight problem was the nosewheel, which brought with it a 300lb weight penalty and a number of unneccessary ground accidents when it collapsed. In this respect, the Airabonita is a more logical layout.
3. Much was made of the complicated control runs, but again, the car-door-layout prevented simpler solutions. With solid fuselage sides, the engine controls could have gone "straight back" instead of "forward a bit, down a bit, back a lot, up a bit".
My ideal mid-engined fighter would have the cockpit moved to the forward position (as in the Aircobra trainers), a decent-sized fuel tank between the cockpit and the engine, two synchronised cannons under the cockpit floor with ammo boxes behind it, and two more in the wing roots (FW-190 style) with ammo boxes in the wings.
P.S. - how odd: I've just been considering a scalorama'd 1/48th to 1/72nd Aircobra as the basis of an alternative FAA turboprop fighter to occupy the "slot" of the Wyvern in an alternative timeline....