What is the point of linked controls? In the event of incapacitation or a dispute over control they present a serious problem.
I've been flying the A320-series for 10 years+ now. The current system does work, but I still believe it would be a major improvement if the PNF's side stick was somehow linked to and moving in the same way as the PF's one. Nobody can deny that would be a welcome feature. Obviously this should not necessarily be a mechanical linkage. An electronic feedback, combined with today's "dual input" warning and priority button would be optimal in my opinion. There's little doubt in my mind that that's what the future will bring. No problems in case of incapacitation in this way either.
(If you want to eliminate the risk of ONE rogue pilot wanting to do something wrong with the plane, I can't think of any other solution then introducing a 3 pilot cockpit each with their own sidestick or yoke where two inputs will have priority over the third pilot. But something tells me that's not going to happen.
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The new Gulfstream and Bae sidestick system looks very promising to me!