Kleopatra currently only supports one smartcard.
This is basically just the smartcard that you get with "gpg --card-edit"
GnuPG supports multiple smartcards / readers at once and I think that this is also a use case that Kleopatra should support.
So the smartcard management should have support for different smartcards with different apps.
Caution for testing: I recently noticed that GnuPG stable did not support more then four smartcard readers at once. For that 0e721b635d6105e1a5b443684116fb9edfe77f92 is needed.