As far as I know, none of the existing post-quantum cryptography candidates offer a viable replacement
crypto_box_seal() functionality. That is: Anonymous public-key encryption.
An example for where this would be useful is encrypting credit card numbers in a database, but only being
able to decrypt them with a key that is kept offline.
An attractive solution would be to use SIDH in place of ECDH, building a similar protocol (i.e. ECDH with
one ephemeral keypair and one static keypair, then an authenticated cipher). However, as noted in
this paper by Galbraith, et al., an active attack against SIDH with
static keys is possible.