I've also been thinking of the practicality of having both a left handlebar brake, & the foot brake, but would also lose the foot brake if needed. (My right foot is partially paralysed, so my rear braking tends to be lift & stamp)If practical, I'd like to retain the operational use of the foot brake, but if that's too hard it'll go to the left handlebar with no regrets!
The system I'm thinking of is having a hydraulic clutch & lever off a suitable donor bike, with the hydraulic hose running to the rear caliper, sharing a dual banjo fitting with the rear brake pedal hose: Not sure if that would work with back pressures through either master cylinder when braking.
For the parking brake, I thought of just having some sort of stretchy band to loop over the lever, when the parking brake is required.
The only other concern is insurance or warranty issues, with changing anything from a standard system.
(After waiting 5 weeks, my Tri-colour is due next week.........:laugh