"Your focus determines your reality" - Qui Gonn Jinn
Firstly, on the matter of ships it's kind of hard to make up something really original and new now, without anyone saying something like "but it's just a ship X with a little more Y and little less Z". What is more important; wake up, game IS finished. It's beeing sold on Steam as a completed product, not beta or early acces or anything else, so basically Muse can just turn all their focus to making new things. The matter of patching or adding new content to the game is their decision. Of course it's in good taste to have some backup (or at least patches) for the game but it's not a must.
Secondly if you'd be enough interested to actually watch chat with devs you'd see that in spite of all that they DO make things for Skirmnish mode. They said that new update will be soon (like a month or so I think) and that it will do some changes to clan system and some changes in ammounation. Maybe more, but I just didn't remember
So be less demanding and more patient, my friend.
Adventure doesn't even have a set release date
Well kickstarter page says it's in some time in 2015. It's hard to set a date because it's hard to tell percentage of work and I guess many things are rather in, let's say thinking-phase than doing-phase.
Look at the suggestions/feedback forum. It is not full of suggestions for Adventure. Its almost all requests for content for skirmish
That's because
1. There is special subject for Adventure Mode suggestions
2. Adventure mode making is in so early phase that even Muse is not sure what exactly will it look like.
Muse is also working to make some of game modes from Adventure Mode to be availible to play in skirmnish, so with release of Adventure Mode there will also be some good stuff for Skirmnish too