I don't understand why you think that others need to benefit from unspent game currency. People leaving game currency in their account likely don't have enough to splash in the market anyway.
Secondly, why would swithcing to bitcoins make the game currency more volatile? The prices are likely pegged to USD anyway, so when price of Lindens to USD changes, price in Lindens change, yes?
So people would just be posting ever changing prices in BTC... same thing.
Thirdly, someone mentioned Linden Lab can't charge fees.... how about they set up a bitcoin exchange? Then they could charge fees just like gox.
I'm guessing it is best to think of ways to have both currencies exist and make things grow naturally.
No one is up for mass change for the sake of change.
1) It is probably true that people leaving game currency in their accounts don't have much. However, I've witnessed many people abandoning land to Linden Labs that is worth quite a bit of game currency. It seems unlikely they would also abandon significant sums of game currency, but it's possible. Linden Labs sometimes cancel accounts that violate the Second Life Terms of Service, and confiscates their assets. Abandoned assets enhance Linden Lab revenue, but it is not known to what degree.
2) Linden Labs makes a market in lindens/USD on their exchange and maintain a very steady exchange rate. That is why there is a big difference in volatility between the lindens/USD value as compared with bitcoin/USD. As a long time Second Life resident, I've been able to keep Linden currency in my account without experiencing any significant change in value (as measured in USD) over a period of years.
3) Yes, I would think LL would be likely to run a btc/USD exchange if Second Life were to switch to bitcoin. However, in the face of competition from lower fee exchanges, it seems unlikely it would be as profitable as their current exchange; and making a market, which is simple for them now (and apparently quite profitable), would become more complex and riskier.
Personally, I wouldn't mind if Linden Labs did switch to bitcoins or added bitcoins as an option. Considering the software changes involved, potential reduction of exchange revenue, and possible disruption to the Second Life economy, I doubt they will consider making the switch unless someone can come up with some offsetting benefits.