I'm on my third aggregator now (NetNewsWire, FeedDemon, Bloglines). All three pretty much present items as a big scroll. Despite some people's protestations, one huge pile of news isn't all that different than a bunch of big piles of news.
But the feeds in my blogroll are diverse, so why not more diversity in presenting them? For example, most of my feeds produce on a human timescale and rate; fewer than double digit posts per day. Then there are few firehoses: Engadget, (old) Scoble, Boing Boing. Now there are synthetic information streams like my del.icio.us inbox which can blow real humans out of the water. For the first category, wouldn't it be nice to have retrospective background information collected and constructed, just to provide context? For the last two categories, I'd like summarizations. Whiffs of AI-hard issues come to mind, but I think a little bit of topic clustering and temporal clustering would go a long way. Not to mention a bit of decent infoviz.
Oh yeah, and with photos pushing their way into syndication why not just tile a bunch of thumbnails?
In a current aggregator, as a first cut users could simply specify an interface preference with a reasonable default. Blue sky, next generation aggregators could adapt to the feed.