Hi Chris,
For me, on a P, would like to see:
Graphite reinforced neck,
Flatter 'board radius (9.5 - 10"),
Lighter weight modern tuners,
Easy truss rod access in the form of a bigger channel routed in the body (Lakland style),
Through body stringing bridge with top load option (Badass 3/Fender HMV),
Slightly hotter p'up,
Quality Passive electronics.
Cheers,
Jon
edit: Spelling!