"etc." should be Number=Plur

[nschneid]

Because (given that we interpret it as a noun per UniversalDependencies/docs#820) it stands for "and others"

[amir-zeldes]

Also note it can have coref with plural antecedents: [[Wang]1 et [al.]2]3 ... [[Wang]1, [Smith and Yamada]2]3