No, there can only be one straw hat left to join according to the canon imposed by Luffy at the end of Chapter 1. This remains constant up to the most current chapter. The pattern has remained fairly the same since the East Blue Five, but since we are approaching the end of the Yonko Saga (unless Elbaf or whatever happens next dispels that notion), I believe that there is going to be one final strawhat. I believe the final candidate is Yamato for first preference but this might not be the case if the author decides otherwise. The question is, out of the selection of candidates, which has the 1) Will, 2) Dream, 3) Role to fit into the Straw Hats. For Brook it was obvious, for the current candidates its more unclear.