I'm not too sure. I doubt they'd remove Isabelle because a lot of people love her and she's really well known, I'm just not sure what role she'd have. I'm curious to know if we're still possibly mayor of this island, but I have a feeling we won't.
For the villagers I'm honestly really hoping they have a smash ultimate approach where they bring back all these villagers from all the old games, even the Japanese exclusives, so that way nobody is left out and combine that with possible new villagers they add in.
I'm going to say none of the ones that appear on amiibo cards will be completely cut - surely they can't expect us to collect all those cards for nothing??
I hope Booker and Copper are in this game....and I want both of them at the same time again. They had funny dialogue, and only having one was a disappointment in New Leaf.
I dunno... I'm sure there's room for all of them. For Reese and Cyrus -- you do build stuff, but I am sure you eventually can purchase furniture as well. Cyrus doesn't build or craft things, he refurbishes them and edits their colors and patterns. So he can still serve a purpose. And even though you can sell things to a Nookling brother, I'm sure you could still sell things to Reese too... In NL you could sell stuff to one of the Nooklings. It just wasn't as good.
As for the police dogs, etc, I am sure that as your town grows and becomes more populated you can instill the basic "town" functions such as the city hall, post office, and perhaps a police station. I just can't see them getting rid of that entirely. And if that doesn't exist, maybe they are airport security?
I really want to see Gracie and Joan, I doubt those two will disappear. I accumulated my wealth through the "stalk market" in NL so it'll be sad not to have that option in NH, though I can't see how it could be quite as sensical of an option... at least at first. (That is, unless there's some sort of marketplace that temporary vendors might make visits to.)
She's not gone. An IGN article confirmed she's in the game, but you need to unlock her by paying off your debts and building things.
Given how stuff seems to be unlocked, I'm not sure if anyone will actually be removed entirely, though I imagine Cyrus and Reese are the most likely candidates given the crafting element. Though if you can and wind up crafting the Nookling shop, I could see them taking over the role of running the crafting services.
Due to these characters being acquired through Amiibo figures/cards, I actually think they will make it since they are relatively easy to get if you have those particular Amiibo. Additionally, they are just another "skin" of other villagers so they should be easy to be added in from a programming perspective. Just my thoughts.