For V2G to scale, international standards must be in place. Until now the only standard for V2G communication between the EV/EVSE was the CHAdeMO standard.
A new standard is underway that will add large momentum to V2G.
The Combined Charging System (CCS) is fast becoming the dominant international standard of choice. A new standard protocol IEC 15118-20 will be released Q3 2021 and will complement the CCS. This standard covers both bi-directional AC as well as DC power flow as well as plug & charge.
It will take some time before IEC 15118-20 will be implemented ubiquitous, but companies have already started to release products with some versions of IEC 15118. The Porsche Taycan can now communicate with Ionity chargers using this standard for plug&charge, the Lucid Motors Air uses 15118 to communicate with IoTecha Corp chargers to provide V2G services (e.g. workplace charging minimizing the combined building/EV electricity cost) and Tritium can provide plug&charge with 15118.
For communication between the EVSE and the backend de-facto standards are already in place (and widely deployed) such as OCPP 1.6 (or 2.0.1) and OpenADR. Work is progressing on a standard IEC 63110, but it will not be available before 2022/2023+.