Looking at bitcoin in term of how we use Fiat I think it's important to do the math a break things down into how we use fiat and the current denominations we use. A dollar is 100 pennies. 

If 1 bitcoin were worth 1 penny for each part or 0.00000001  = 0.01 usd then bitcoin would be worth $100,000

If 0.00000001  = 1 usd Bitcoin would equal 1,000,000

We've already had discussions about getting rid of the penny but how would that look? If we kept the nickle and quarter we'd still be having intervals of .05 usd. Which you couldn't pay out with bitcoin in change. So that change would have to be lost in day to day use (if it was used that way).

Looking at the world from the perspective of a citizen of the United States makes me think of things in terms of the USD. That being said it's hard to view something reaching a value that cannot be broken down to a penny as a currency. If bitcoin hit 1 million what would we do with the extra cents? Perhaps that's where litecoin would come in or possibly that's where we'd have another currency that could replace bitcoin to give that level of value. 

I think that bitcoin hitting and sustaining 1 million dollar value is at low odds unless we all agree to drop the last decimal of our viat. Making the usd worth 10 1/10th pieces (dimes) at it's smallest.