I'm sure Shaun has thought about this but I think it would have worked really well as hosted solution with free and paid accounts. I'd be more than happy to pay $10 a month for Fever as I've been looking for a way to sort out RSS feeds in this way.
I hope it does well though, so that it will be worth his time to develop a desktop platform or something I can just purchase from the Apple App Store. (Hopefully both.)
I think Shaun's $30/one-time cost + you deal with your own feeds is a really smart approach. Wish I'd have thought of it.
I'm sure he also enjoys sleeping without having to worry about server downtime :-)