Chung's "references" are a couple of like-minded people on Usenet and his own inferences, but unfortunately his inferences are very limited. "No stealth in space" is more or less a normative statement. If you define "stealth" as "retaining the ability to surprise," then stealth is possible anywhere. Even in space.
If you define "stealth" as "a limited series of technological/physical solutions to solving a problem," or "never being detected," or something equally narrow, then stealth is only possible within certain limited constraints and environments. Hiding in the Antarctic would be near equally difficult as vacuum by the latter definition, which is why no one serious uses the latter definition. It's too contrived. I suspect the association of "stealth" with "technological solutions" comes from people reading about VLO aircraft and thinking that emissions control is the only kind of "stealth".
That's the point, though. You have to be looking in the right spot at the right time. You have to have Sufficient Optics to get enough detail of what you're looking at to make an analysis, you have to have sufficient operators (or sufficiently powerful computers) to synthesize this information into useful targeting data, you have to know ahead of time where the enemy is going to be, etc.
All of this takes time, which is something the enemy can use to confound efforts to detect, track, or attack him. It only really applies when the target you're attacking doesn't move, can't defend itself, and doesn't bother trying to hide. Coincidentally that is pretty much every modern spacecraft.
Orbit around celestial bodies is the only thing of military value in space, at least in any "realistic" setting it would be the only place battles would (or even could) be fought, which means X-37B has effectively achieved stealth in space by virtue of having a giant object (Earth) to hide behind while it does orbit changes. You think you see it, you setup an ASAT launch the next time it comes around, and then it's not there when you look again, because the spaceplane changed orbits on the other side of the world.
If you're going to start complaining about "the laws of thermodynamics" or something in a setting where literal time travel exists, then you've much bigger fish to fry than a couple spaceships not cooking their contents to well done.
It does if you don't know where to look. Considering you need to search a large portion of sky to find even one satellite, imagine trying to keep a real-time picture of their movement if they were all switching orbits constantly and usually out of your view. It would be difficult to impossible.
I'm not being rude but I guess you could say blunt. Dramatic or obviously wrong statements like "crossing the line" and "no stealth in space" are a bit silly, though.
A better addition would be some sort of espionage or fleet intelligence that lets you see what modules enemy ships have, what ships they're building, etc. The picture would be patchy or prone to errors, like in Darkest Hour where you can get incorrect estimates of infantry divisions or build queues, depending on how much funding you put into it. In Stellaris case, it might be incorrect or unknown ship modules, and incomplete estimates of ship numbers. Ultimately though, you'd be able to see all the ship types your opponent has in service and their modules, so you could plan how to counter these specific ship types.
Misdirection wouldn't be terribly useful given this is a grand strategy game. Being able to mask fleet strength can already be done, technically, if you optimize a build. Optimal build ships tend to belie their true strengths substantially.
It might be possible to work in a fairly wide intelligence and counter-intelligence system where you'd feed players false information and obtain true information, or vice versa.
I'm not sure how the diplomatic screen makes the "fleet power" judgment, but being able to change it actively would be interesting. You could provoke opponents into attacking you by portraying yourself weaker than you are, etc.
