unwrapped CBOR tag number 1 for validity?

If CBOR encoders and decoders already support unix time it removed one of the reasons to not use unix time.

unit time does not support leap second, but we could probably live without.
how to differentiate between utctime and generalizedtime? RFC 5280 states that UTCtime shall be used before 2050 but this is not always followed (e.g. Brazil has a cetificate policy stating that GeneralizedTime is always used). Do we care about implementations breaking RFC 5280?
If we ignore leap seconds and mandate following rfc 5280 the encoding size of the current unwrapped biguing and a unwrapped tag 1 would be the same.

cose-wg / CBOR-certificates