777 Folding...
Starting from a clean aircraft we have:
Civilian aircraft with
Retractable gear
Retractable flaps
Retractable slats
Speed brakes
Variable position tail mounted air brakes
Powered flight control surfaces
Thrust reversers
Variable pitch props
Military Aircraft with
All the above plus
Flight opening tail ramps
Folding wings on ground/board
Variable Sweep in flight
Retractable flight refuelling equipment
Add to the list as required - all of these items operate in the air flow and affect aerodynamics and possibly structural integrity.
They are all long since accepted as normal.
What will be more critical than these with a folding wing tip on an airliner? Not the reliability or feasibility.
Ground handling in case of failure in open position may present a problem depending on airfield - but there will be procedures to deal with this condition.
Even better, The tip will only be actuated (extended / retracted) on terra firma, unlike some of the other accepted items which can cause in flight problems.