And wasnt that thing at the left side of the Kol its hangar bay before? Where did it go?

I mean if the advent look clean, that would fit their style right? But TEC were supposed to have repurposed old trading ships for the job afaik with I guess the Kol being the exception. But maybe the people in charge of the design are not the same as the ones before so they might not have noticed the details (like your mentioned adaptive shield generator for instance)...

It would be indeed cool if you could research like an "overhaul" to the existing prototypes. So for example the first time you build it it is kind of a prototype ship, like in the original and if you research "advanced designs" or something like that you get the upgraded version... but you are right, its too early to speculate what the final product will look like!

I agree, TEC ships should have their own style, and btw, are the vessels around Kol in the picture Javelin?

Yeah that's a concern for me, the first game had a very realistic art style and design, Sins 2 seems very cartoonish from the banner with the characters to the ships being so colorful. I don't mind it looking clean, in 5 years we're not sure what advances have been made but I'd prefer the team colors to be more subtle. The character designs though, this looks like they pulled them from a Nickelodeon cartoon show.

I agree with the Star Control: Origins comparison — such an art style works fine there, but not in Sins. At the very least, is it possible to make the ships have a proper metal look and feel instead of what is often described as “plastic”?

Still, I am more concerned about gameplay than about graphics — these can always be modified with a mod. Just take a look at Sins Remastered.

I think the only reason people think that the units look "cartoony" is because of the larger team color spaces on the units, and the relative lack of weathering effects compared to how motley and dirty the original TEC ships were. However, for certain other units like this new frigate (the updated Cobalt?) it's clear that shape-wise the designs still look "realistic" once the team color spaces are relegated to stripes or small spaces, since they still have lots of sharp angles with immense amounts of surface detail. I'd call them "cartoony" if they suddenly gained lots of softer, rounded edges to otherwise blocky designs with more exaggerated features with less detail, as in the case with games like Command and Conquer 4, and that's simply not what I'm seeing from the screenshots. Even the Kol battleship image used as the OP example still has a good amount of raised surface detail on it, and just a change in color to the new Kol battleship changes its impression entirely, as shown by this particular screenshot. 

How do you even measure "realism" in terms of proportions for a sci-fi game anyway? Nothing I've seen out of the current ship images suggest any exaggerated proportions. While I've seen people whine about the large turrets on the new Kol - a complaint I don't understand myself since the turrets don't look large or "cartoony", I keep asking myself how its size relative to the ship is any different from say the Kodiak's (non functional) turret back then. I've seen people claim that the "large" turrets are also "unrealistic" somehow, despite the fact that we're talking about a sci-fi setting here that doesn't exactly stick to "realism" the hardest. 

The "clean" part is the only complaint I get, and one I've already explained in my previous post. Even then though, that's an easy enough fix if the art team just add the more "plated and dirty" texture of the original ships on here. Even without such though, the surface detail on the ships combined with their general shape more than prevent them from looking "cartoony" to me, at least when they are looked at by their own merits and not compared to the previous game's TEC ships.  

"Realistic" vs "Cartoony" in an RTS is something like the difference between Dawn of War II vs Dawn of War III, or Tiberium Wars vs Tiberian Twilight. This is hardly such a difference in my eyes, and I personally don't have an issue with having more "clean" looking ships (always been more a Star Trek guy than a Star Wars one). Now if these ships somehow sway when moving with turrets that pointlessly bounce, then we can talk about "cartooony", but as it is there doesn't seem to be any indication that they're going down such a route.