Does sequoia support or aim to support yubikeys (or similar) at all? That was one of the great selling points of gpg for me, which I use (with pass) as my password manager, and occasionally for email.

Yes. Sequoia abstracts over secret-key operations. In fact, the Octopus makes use of keys managed by the gpg-agent using this mechanism.

Native support for smart cards and TPMs is planned and being worked on.

This is awesome. So excited for this!