Implementation of net metering is hampered for two reasons: the degradation of batteries, which means they would need to be replaced more often, and the EV has to connect to the grid in the same way a solar photovoltaic system does, complying with standards to protect line operators and maintenance personnel working on the grid. Bidirectional charge controllers add to costs, but EV manufacturers such as Tesla and Nissan have now taken steps to enable vehicle-to-grid connection with some of their models.
Additional charges for enabling the export of electricity from households, as well as the buy-back rate of the electricity, depend on electrical utilities and pricing arrangements/regulations. Further details are outlined in the article linked below: