If you are a priest, you are a priest. Ordination is an indelible mark upon the soul such that even a priest that has been laicized by the Church (removed from his office as a priest) retains the ability to perform the sacraments (though he is bound by the Church to only provide the last rites in emergencies). To separate the priesthood’s duties amongst married and celibate priests would be injurious to the office of priest, especially in the mind of the laity.
On the other hand, however, we already have such separation. Deacons receive ordination but not the full ordination of the priests (who in turn do not receive the full ordination of the bishops). Deacons are not required to be celibate.