There will most likely be new fielding metrics which make today's metrics seem silly. However, there will be no way to evaluate the players of today because the data used in the future won't be available for today's players and certainly not players who played before statcast.
I don't know how much more they can do with offense as far as evaluating results. There will be better predictive and scouting tools, but I think the results metrics for offense won't be that much further advanced. There might be some tweaks using more situational data, but I don't they'll be questioning today's great hitters.