Ingram and Hopkins haven't been playing that badly recently... And Broom will come in 4/5 so hopefully he can play better. The selectors probably wouldn't want to bring two new players in at the same time against Australia.
Yeah this, would be careless IMO. As much as I want Williamson to play for New Zealand I wouldn't want him coiming into a team filled with guys that have yet to do anything at this level.
On Hopkins, yeah he's been pretty good but as crazy as this might sound right now I'd back Broom to score a goodish total (60+) then I would of Hopkins.