As per the specs changes - open-telemetry/opentelemetry-specification#3184, Unit should used in Instrument selection criteria defined in View API.

Changes would be potentially required here - https://github.com/open-telemetry/opentelemetry-cpp/blob/main/sdk/include/opentelemetry/sdk/metrics/view/meter_selector.h