"No non-STOVL land-based design has EVER been developed into a successful carrier-based variant."
Yeah, right. Look at failures like the Hawker Nimrod, the de Havilland Sea Hornet, the Sea Venom, the FJ-3 Fury, the Sea Vixen (DH110), the T-45, the F/A-18, the Su-33K, and the MiG-29K.
"Oh and the various Heath-Robinson concepts already wheeled out to get typhoon to be CV-compatible (periscopes anyone????)"
Yeah, right. Your second generalisation is almost as incisive as your first. Typhoon N will clearly be compromised (there's a 300-500 kg weight penalty, depending on the options exercised), but the commonality benefits are considerable, and it will be supportable, sustainable, operable and upgradeable without US say-so.