There are many indications as to the first expantion being set in Pacifica.
My speculation is it will be playable during act 2 and will include gigs, blue events and a story arc, asside from all sorts of assets (weapons, clothes,...).
Going into pure fantasy based on that speculation I I'd really like the story to go further into the AIs, the Voodoo Boys, the deep net and the Black Wall, Alt herself and the other AIs, the Bartmoss viruses,...
Morgan Blackhand would also be great to learn more about in 77, Mr. Blue eyes, Peralez, more about River especially (from the LIs)...
What I don't expect them to do in any of the expansions is to set them elsewhere than Night City. Opening closed spaces seems much more resource efficient to be able to focus on other things, Night City is already amazing so finishing touches are way better for me qualitywise too. With exception to some additional closed space set outside night city for some specific new quest.