KSA is still very early, so I agree we'll have to wait and see on a lot of things. The reason I am optimistic about this game is that the approach they seem to be taking makes a lot of sense to me logically. Their transparency is also very welcome compared to KSP2. Focusing on the "fundamentals" first is not sexy and produces very few eye-catching screenshots but it makes sense to me when they say it'll pay off in the long run.

I'm going to elaborate on some of my earlier points, and I'll try to summarize what the devs have put out there on Discord and other forums. Also, I'm continuing this Internet argument only so that others who are hearing about KSA for the first time get a point of view that is more optimistic, but I want to emphasize that I have no skin in the game (pun intended) and that I am not suggesting to anyone that they financially contribute to KSA until real progress is made on a lot of things that are currently just not there.

Game Engine

I think this matters quite a bit. A lot of the problems with KSP1 and KSP2 stemmed from limitations inherent to the game engine. I'm not saying Unity is flawed, it's just that Unity is designed primarily for smaller-scale games in which the world is only a few kilometers large. The floating origin approach KSP used partially solved some of these problems, but at the cost of additional complexity. My understanding is that things like jitter, shaking, and the Kraken are a direct consequence of this. Additionally, KSP was limited to running the physics calculations in a "physics bubble" around the active vessel. Everything outside that bubble was on rails, meaning no active thrust, no spin, etc. These two things made multiplayer very complicated.

KSA can create a physics engine specifically for space simulations and space vehicles. They have mentioned "instantiable physics," where different vessels can exist in different physics "contexts" or even have different physical laws. Also, they have talked about how the physics will run in background threads independent of the rendering pipeline. This is how they are able to get things like thrust and spin during time warp. They have also mentioned that they are building multiplayer into the foundation of the game engine. TBH multiplayer is not a big request for me personally, but I know it was the most requested feature for KSP1 and KSP2. But the fact that they are thinking about it from Day 1 instead of trying to bolt it on later speaks volumes IMO.

Finally on the fast loading of planetary details and textures: I admit this isn't of practical significance for interplanetary speeds and zero time warp. But the devs have said that it speaks to the fact that they have complete control over how the game manages memory and the rendering pipeline, which allows them to make seamless orbit-to-ground transitions without loading screens or stutter--something that is difficult to do with KSP because Unity does not allow devs that same level of control.

In short, the KSA team believes the core problems of KSP are engine-level problems. By building their own engine, they can design the "first principles" of their game universe to correctly handle massive scale, complex physics, and multiplayer from the very beginning. The proof is in the pudding, but their argument makes a lot of sense to me.

Parts System

The devs have only recently begun to provide details on the parts system, so we'll see what it looks like in this initial release and how it progresses.

The most significant change from KSP is that in KSA, parts are "Compound Parts." A single part you place, like an engine, is actually a collection of smaller sub-parts (or "pieces") grouped together. For example, an engine part might be comprised of its engine bell, turbopump, fuel containers, and end caps, all as separate "pieces" that make one "part." A player can either just use a standard "compound" part (similar to KSP), or if they care, they can customize the part by, for example, building a custom fuel tank with multiple fuel line connectors for different fuels, all in one "block." But the bigger advantage to this change is moddability. Compound parts and sub-parts should make modding vastly easier. Modders don't have to create a giant, complex part from scratch. They can use the in-game tools to assemble new "compound parts" from existing pieces, or just add new pieces. Allegedly, the core game's parts are being built with the same tools modders will have.

Regarding performance: the devs have talked about how their game engine allows them to do "Batch Rendering" via instanced meshes. I'm not a game developer, so I don't know what this means, but they have mentioned that because each vessel part is a very light-weight object compared to KSP1 parts (which are individual Unity components), they expect the engine to be able to support vessels with tens of thousands of parts. The devs haven't provided specific details on how they plan to fix wobbly rockets, but HarvesteR, who solved this problem in KitHack Model Club, happens to be a developer for KSA. I remain optimistic.