Puerto Rico's population is around 3 million, less than a percent of the 331 million population of the US. I wouldn't expect more than a slight change to the graph either way.
South, but potentially east a little too. (PR is further east than all but parts of Maine).
Right now most of the Bay Area is barely to the south of the median, so I suspect the 2030 update won't change much there. As far as east-west goes it looks like it's in the middle of Chicago right now (which also helps explain why 2010-2020 didn't move that far west).
I brought up the Bay Area in terms of the medium because someone moving from the Bay Area to Hawaii would have zero impact on the median population longitude. However, it would impact the mean population longitude
Just noting that since the Bay Area's pretty heavily populated, bringing in Puerto Rico (shifting the US median south by ~1.6 million people) takes the median from say Napa's latitude to, say Alameda's latitude (keeping in mind that there's also Louisville KY and other smaller non-SFBA towns in the same band of latitude).
