The components of the zone system which are appropriate to visualisation and determination of exposure are just as valid to me as they ever were. True, I no longer need to make exposure judgements based on how I will develop a negative, but I make them bearing in mind how I will post-process. I also think that as a framework for visualising relative exposure values in the scene it still has value, remembering that the camera meter (grossly over-simplifying the sophisticated technology here) will place exposure on zone V.
That said, I think the sainted Adams would have loved the RGB histogram - I know I do. For me it's the single most valuable aid to picture taking that has been introduced in the last 20 years. I never liked Polaroid backs - they gave only a rough guide to lighting at best, and were poorly representative of how the film / transparency would be exposed.
A fundamental tenet of the zone system is that you determine exposure bearing in mind how you will develop the negative. This is still very true, modified for the characteristics of the sensor and how you will post-process the RAW - exposing to the right to preserve shadow values / lower noise is an application of that, as is taking mutliple shots for blending.
As a rule of thumb I still spot meter off a caucasian face and dial in +2/3 exposure comp for portraits!