If that servo fails to unlock, though, now you can't shift into certain gears. I thought that a centrifugal clutch disengage mechanism would solve this. Centrifugal clutches are already common in scooters - the clutch engages gradually as you rev above idle rpms. My theoretical feature is basically the opposite: a centrifuge that disengages at a given RPM. You _can_ shift into 1st at 100mph but your clutch will quickly disengage as your revs approach redline. You may burn out your clutch but those are cheaper to replace than engines.
Of course I have zero mechanical engineering background so who knows the feasibility of this approach.
Re-engineering the clutch sounds like a lot more work than adding a little servo. (Or two: one for 1/3/5 and one for 2/4.) And yeah, like anything in the car I guess it could fail, but something so simple could be made very robust—and if it did fail, it wouldn't be catastrophic. Would also be simple enough to add a mechanical override screw accessible under the shifter boot or something like that.
Of course I have zero mechanical engineering background so who knows the feasibility of this approach.