Alright, here's what I've got so far.

Constraints:
1. The web as it exists today is largely slanted toward clickthrough. Yes, this means that the Reddit Comment Model dominates, but it also means that the content users link to is sensationalist and, frankly, poor quality, because the publisher doesn't much care how long the user stays, only how many clicks they generate.
2. Content vs. comments. In my web forum experience, which is more extensive than I'd like to admit, form factors tend to favor one or the other, either in terms of quantity or quality. There is no such thing as a high-quantity, high-quality forum; if there were, you wouldn't be trying to make one.
3. Growth vs. loss of cohesion, aka the Eternal September problem. I've seen this solved only twice in countless tries, but each under very unique circumstances. (One of them is r/SRS, which I think is a bunch of silly people, but they've both grown a lot and kept being exactly what they want to be, which is something virtually no online forum can say they've accomplished.)

Potential exploits:
1. Your name, The List. You're not a bunch of submissions that happens to appear in ranked order, you're The List. How many items are on The List each day? If the answer is infinite, not much thought went into making the list, which means you aren't a site that rewards depth. One alternative model: Take link/topic "requests" and let users vote on which will appear the next day. This avoids the ever-present problem of reposts, which is what drives away longtime users fastest. Whatever, say, 7 topics win, those 7 items are linked and up for discussion the next day. Losers are cast into the abyss and nothing from that domain can be resubmitted for another week. (Or you could just hand-pick from among the requests. Whatever.)

2. Lack of time-sensitivity. You're trying to be the opposite of the 24-hour news cycle. If somebody has a thought-provoking piece from 2001 about 9/11 (like Hunter S. Thompson's take on the event), then awesome! People would love to see that. But it'll never match up against Fox, CNN, et al., who put food on the table by shortening your memory. So don't let them compete. No news. Fuck news.

Why I think the above can defeat Eternal September:

First, to characterize the problem: it is not people. People are never the problem. People are largely whatever situation you put them in. Eternal September was Usenet's fault, not the fault of incoming college freshmen, as former Usenet folk like to claim.

Take it out of the internet context. What's something else people get sick of? And then are super surprised to find out later that other people are into? I.e., the same way people get into Reddit, enjoy it, decide it's declining, leave altogether, then vomit when they hear it's getting 5B pageviews a month?

Music. Top 40. Whatever you're listening to when you're in your teens/20s, you're going to be listening to the rest of your life. But it's not like the Backstreet Boys were so much better than Justin Bieber. (Let me tell you, the people hating on Justin Bieber now freaking loved NSYNC, and I've got the photos to prove it.) It's just that after listening to X amount of music, your tastes are established, and everything new after that sounds the same because it all sounds sufficiently different from what you're used to.

How do you defeat that? Change the form factor. No more radio. 5 songs a day. They better be fucking good.