So, I decided to make the complete list of changes (i have noticed) that SimplePlanes 2 will bring. The sources were the video trailer, and screenshots from Steam. If there are any other sources of information about SP2, ping in the comments so that I can update the list

Note that this is my guesses are based on what I could notice among the information in the public domain. Some things may not be in the release of SP2 or will be removed. If you have noticed any contradiction, you are welcome to comment.

Interface

• Interface elements (panels, buttons, etc.) will now have rounded edges and softer colors.
• You will be able to pause the game without opening the menu (I'm not sure about this, but it was shown among the screenshots)

Editor

• The editor background in SimplePlanes 2 will be a hangar
• Now you'll be able to move parts using XYZ arrows, right in the viewport (seems like it will be an alternative to specifying coordinated as numbers. Aso it can be applied to rotation, or even scale, but last part is my suggestion)
• Better painting job: now beside solid color you can assign one of suggested texture layouts to parts and set color to elements of pattern. Seems like texture will override the connections between parts which it was assigned to, for smoother look, which is really amazing)

Parts

• Procedural Jet Engines (Thrust Vectoring was already show in a trailer but seems like there will be more settings)
• New wings. It will have an aerofil profile and working control surfaces by default
• Guided bomb. Seems to be equivalent of default Bomb 50 but with passive homing. Probably inspired by look of GBU-12. In-game name: Lazy50
• New Air-to-Surface missile, equivalent to Inferno inspired by AGM-65. In-game name: Inferno2
• Screen part with real-time camera output (Many questions about this, but for now announcement trailer demonstrated a screen in the cockpit, with target lock in night vision filter)

Environment & Effects

• New map (It is a group of 4 islands located close to each other, two of them are connected by an isthmus. Each of them is close in size to the islands from SP1. The trailer clearly shows a city and an oil factory. Parts of the islands shown in trailer & screenshots are surrounded by roads, which may indicate that the developers are paying more attention to ground infrastructure)
• Water surface will become dynamic: waves will rock your ship and there will be probablymore attention for shipbuilding in general.
• Underwater space will be playable. Apparently, parts specifically for the underwater space will be added (screws, systems for controlling the dive, etc.)
• New explosion effect: animated 3D model of explosion instead of particle system.
• Dynamic lights: now explosions and lights are actually illuminate the space
• USS Beast group updated: now Destroyers look modern, also Aircraft Carrier has 2 catapults
• Volumetric clouds (interactable clouds that can have shadows, and receive fog and volumetric light)
• Ambient Occlusion (Basically, darkening corners and connections spots to make the surface appear more relief and realistic)

Gameplay

• Multiplay (yay!)
• Characters (It's pretty unclear what exactly they'll do, but from the trailer: aircraft carriers and other objects can get NPCs. Planes can now be controlled by a playable character (hello Chad). One of moments at thd trailer shows playable character outside of the transport, marked as a cockpit (essentially an object controlling transport control) with animation of dance, which points to suggestion that pilot can leave the transport and get into another. At the same time, at other moments of the trailer, the cockpit was marked in another part of the plane even with a pilot in it, so its role is still ambiguous.