I think the /new form itself is fine as implemented today. What's missing in the current implementation – but present in this comp – is the "Add content" button at the top of the right rail. I'd expect that to be present when I'm logged in and looking at a specific magazine, and I'd expect it to link to /m/<magazine slug>/new
A similar button is present as part of the instance-wide intro box that atop the right rail in a logged-out view, but it disappears once I log in and there's no equivalent button in the magazine section.
I also think this comp's stronger treatment of the "+ Add" button in the global nav bar helps by making the button stand out a little more, but it's still grouped on the right side of the global nav. The problem is that everything else in that area of the nav is a global, instance-wide action, so intuitively it's not the place we look for a magazine-specific action like adding a new article.