Are there really enough good companies out there to justify four cycles? At 20 companies per cycle, 4 cycles per year, 3 cofounders per company, $6000 per cofounder, that's $1,440,000/yr for roughly a 5% stake in each company. Just to break even, these companies must end up being acquired/liquidated/taken public for a total of $28,800,000... a very high threshold. Given that YC has only had two or three successful acquisitions (Reddit, Parakey, ???) and only one extremely successful still-private company (Loopt), I'm not sure that YC could beat those odds with four cycles per year.
BTW correct me if I'm wrong about the number of YC companies that have been acquired or are doing extremely well... always happy to hear success stories.