I never said primecoin would fail in 5 years, what I mean is that it should give us a better overall grip at the market in the next 5 years. It is designed to last longer, as long as bitcoin and litecoin that is. I would not say this is sort of 'WMD' to bitcoin's dominance, that would be arrogant for me to say and I have too much respect for Satoshi and the current bitcoin development team. It's really a tool to help us position against litecoin, which now has a too strong momentum for ppcoin to challenge by itself alone in the short term. If primecoin is successful, it could demonstrate the limitation of pure proof-of-work systems and help to level the playground faster.
The thing that perplex me somewhat is that, there are many decent developers and other talents around, but at this point most of them just want to start their own clone coin. I hope this is just a transient fad because of the recent success of litecoin, and later on people would realize it's more fruitful to just take a stake in a good coin and join an existing capable development team. For example, talents like Robert (dreamwatcher currently running explorer and leading JKC), and like Peter Bushnell (currently leading FTC who seems to be good at marketing and management), and many others who are capable of doing apps like basic auction site, escrow, games etc that think they can clone a coin and then leverage their app skill on it. In my opinion if the app is that good you don't need to start a coin, you can just support most popular coins out there already and become a market leader for that particular app.
I believe as we approach 100 altcoins competing in the market soon the attitude in the market would change a bit, then we would be able to see more talents interested in joining ppcoin/primecoin team.