All currencies, FF miles included, run on faith. If people no longer believe a peso, or a baht, or a mile, is worth anything anymore, voila! It isn't.

Because their supply is steadily increasing, they are naturally worth less over time, and their precise value on any given day is a sort of a lottery (can you redeem in F to Bali this afternoon? Maybe yes, maybe no)... a crisis of faith in FF miles, and an inevitable currency crash, is practically guaranteed. This is why hoarding is stupid, earning-and-burning smart.

You're already seeing people drift away from certain airlines because redemption is difficult and the rate tables are so daunting. Look for that on a grand scale. At some point, when Bali is 500,000 miles, you're earning them @ 50,000 a year, and they expire in three years, you won't care anymore.