I fully support it deserving a campaign, it really does.

I have thought about this a bit. I think a campaign should follow the timeline; The Timeline of Sins of a Solar Empire II (sinsofasolarempire2.com) in broad strokes. I think it would be good to play as the Traders/TEC for most of it.

Start with a calm map, teach people the basics of the game. At the end, the Vasari arrive. See how not-militarized the Trade Order was, and have a second mission involve the establishment of the TEC. Keep introducing new ships, technologies, abilities etc. The next step is where the Advent get involved. See the TEC get pushed further and further back.
That nicely leads into the first expansion, entrenchment. From there we can go to diplomacy, start to manage each other and the pirates. Then we move onto the split within the factions, and titans. From here we can include other factions. I would put the end point currently at a mixed faction, where the Vasari Rebels take the initiative and lead a part of the TEC that is not hellbent on wiping everyone else out or bunkering down by themselves. The Advent Silent Ones, or a(nother) third subfaction can also come into play here.
Finally, make them escape, right when the secret threat that has been following the Vasari for 10 000 years arrives in Trader space. Or, get that secret threat to the forefront of course.

I'm not a storywriter at all, and I'm not sure on characters or a cohesive plot through the story that is not just the history as stated in the timeline. I think there's a lot fun gameplay there at least, while also teaching people to play and including lore.

Pretty much all the lore can be found here on the website, in the Rebellion manual included with the game and in-game itself (in the form of features, artifacts and descriptions of other gameplay elements).

Campaigns are horrible in space games...go here defeat that ship...go there discover lost abandoned ship etc.....

Once and done.

Homeworld and it's many players would disagree.

Just for the sake of tallying feedback, I would also put a campaign on the bottom of my priority list.

If it's something that the devs 'really' want to do and it's not likely to compromise improvements to the existing modes, then that's their call to make of course but for my part, I think a scripted campaign in a game like this would be a complete waste of time and resources that I'd much rather see put towards improving the existing modes and variety of content. 

If achievement statistics are to be believed, campaign completion rates for most modern RTS's that I've seen have been abysmally low (including Stardock's own AotS games which rest somewhere between 5 and 8%).  It's a lot of work to put in for a mode that most players are likely never going to see through.

Even if it was, campaign completion is still on the lower end of achievements that owners who actually bothered to play the game came away with.  I realize that, like concurrent user stats, achievements don't paint the whole picture but in the absence of complete data, it's the best easy-access indicator of player behavior that I'm aware of at the moment.

And anyway, putting those stats aside, if IC/Stardock had come into this project with a compelling story that they were eager to tell and had a campaign planned from the get-go, I wouldn't argue against it.  But if it's just something that's going to be thrown together after the fact to check a marketing box, then personally, I'd rather they didn't bother so those resources could be used elsewhere (ie in modes that I'd actually play more than once, if at all). 

A campaign borne of weary obligation to a bit of feedback on the forum isn't likely to be worth the trouble if they weren't interested in doing it to begin with.

Not like I'm against a campaign, but I do agree that I can't see it being worth the investment. An RTS campaign is in a weird place where it has to be really good to matter at all, and it's not going to be unless that was a core focus of the game, which it clearly never was. 

That said, I do enjoy the middle ground of some stand-alone scripted scenarios. No idea if the market is there for them but I'd absolutely buy some DLC scenario packs in the future, Ashes had a couple of these as I recall. If the tools to consider that in the future are in place, that's really all I'd hope for.