Bitcoin will never be the one and only crypto currency. Todays 95% marketshare of BTC won't last long, so when investing in crypto you get far higher returns (at much higher risk) on altcoins than BTC. LTC is the most common altcoin and already established as BTC's little brother. When btc holder start diversiving they will rather buy LTC instead of every other altcoin.

So there is no new risk. Nobody knows if PPC's POS will work for ever, but cloning a already "proven" technology is safer than inventing new one. I liked the idea of DVC but it failed and everyone invested it it will loose. It's a good idea to risk some money at new crypto, but that isn't for diversiving more than 5% of your portfolio. And the rest goes to ...?

Scrypt will be a total different mining enviroment. Once it's really established there will be specialized chips for BTC and specialized chips for scrypt. This makes LTC more independent (=better) and protects it against big goverment attacks. PPC would be ideal for that, but it isn't ready yet.

Bitcoin isn't superior enough to altcoins to justfy a 95% market cap. It might not go down in Fiat/BTC, but in Altcoin/BTC it's doomed to fall.