If anyone wants to see the descendant count now, rather than waiting, I've submitted a snippet of javascript as a Show HN: https://news.ycombinator.com/item?id=27442644

Or just open your browser console and run the JS directly:

  [...byTag(document.body, 'a')].filter(x => x.innerText == 'more').map(x => { x.innerText = `${byClass($(x.href.split('item?id=')[1]), 'togg')[0].attributes['n'].value - 1} more`; });

I find it much easier to browse HN now. It's immediately clear whether I'm missing a large subtree.