Not a death sentence obviously, a second might work, hell even a third if lucky
I'm saying this from my perspective as a possible backer (Obviously I only represent people with the same personality as me). Here are some issues that pop in my mind when I think of making a new kickstarter for each dlc
-Kickstarter fatigue (imagine if it becomes popular and other games do the same as well)
-Little reason to donate (let other people do it, my money won't matter) (mostly psychological)
-Having to think of new rewards and prepare a new kickstarter each time = lots of work
-More likely not to like that particular dlc idea
The advantages I see for putting all DLC ideas in a single kickstarter
-You can put all the dlc ideas you want and make people vote for which ones they want
-More reason to donate (Oh god, This DLC would be so great but it's the third most popular. Here's $5!)
I also see possible advantages for making multiple kickstarters. Frequent exposure might increase interest and the possibility of stretch goals for particular DLCs might make it enticing to donate.
Truth be told, I have a hard time predicting which would have the most success. I know that personally a bigger kickstarter with all the dlcs would increase the odds of me donating dramatically but I am just one person. Do I represent the minority or the majority?
I think the only way to find out would be trial and error
I've thought about it some more and I think the biggest problem I have with a single DLC is the lack of possible stretch goals. Those are very important, they allow people to dream of what could be and make them want to give more. You can't really put many stretch goals on a dlc because you run the risk of turning it into an expansion, which would take much longer. Instead of having 1 dlc every 3 months, you might end up having to wait 9 months for it because it got stretched to 15k. It would also allow for more diversity.
I think what I'm advocating for is to make other DLCs as stretch goals instead of making the single one bigger. And even if out of the 6 ideas only 2 are funded, there are no reasons why you can't make another kickstarter campaign for the remaining 4 once the 2 are finished.