The ground textures weren't streamed previously, but buyable mod packs allowed at the time near photo realistic imagery of the ground - I don't know how it works, but there might be a case of you could replace the streaming textures with local files.
Airports and maybe cities will most likely receive mods to improve building textures and layouts.
The main mods will be for aircrafts, with new liveries and potentially more planes.
It is an incredibly niche market, but clearly makes Microsoft profit and I don't know how it will work on console, but I would say you certainly need a flight yoke or very least a force feedback joystick to make the most of the game - But again Microsoft will release a new controller in time for release on Xbox.
When the last version Microsoft Flight Sim X was released and I worked in Game at the time, we used to have some guy who came in whenever new scenery and plane packs were released, and he used to spend £100 - £200 a time and not seemed bothered by paying that much money out.
It is a niche market, but it really seems like the type of people who play these type of games are the type of money no object people, and the majority will probably very happily all be buying the Deluxe Edition.
I personally wouldn't buy all the equipment to play the game, but if I could play any game VR with a full setup this would be it - Well at least until they release VR Leisure Suit Larry.
EDIT I FOUND SOME OF THE PACKS THE GUY USED TO BUY:-
https://www1.getmapping.com/webshop/Web/Home/Static/ProductsAndServices/Simulation.aspx