Evolution of the response of the CMS ECAL, and upgrade design options for electromagnetic calorimetry at the HL-LHC

The performance of the CMS electromagnetic calorimeter (ECAL) has been continuously monitored at the LHC. The evolution of this performance is a critical issue for the future. Work has started to assess the need for possible changes to the detector to ensure adequate performance for High-Luminosity LHC (HL-LHC) operation, planned for 2022 and beyond. Results from CMS running, beam tests and laboratory measurements on proton-irradiated crystals are combined to predict the performance of the current detector at the HL-LHC. This is achieved using MC simulations of the CMS detector, where the ECAL response has been tuned to account for the aging of the detector components. In addition, various R{\&}D studies are presented in case modification or replacement of the ECAL Endcaps is needed for the HL-LHC period.