pipe dream. other crypto currencies would pop up, which would bring down BTC value.
blockchain confirmations take too long for BTC to be ubiquitous.
Off-chain transactions could make BTC viable in the future. For now, we're no where near the point where BTC is going to be used for in person transactions. It's pretty ironic that people think that shorter confirmation times are a benefit for alt-coins. Reducing the confirmation time makes blocks less secure, and other cryptocurrencies don't have anywhere near Bitcoin's hash rate.
when you're paying for that $5 sandwich at subway, i doubt you as the subway (or say gas station) manager or the customer, will care that bitcoin is in theory "more secure." i think there is enough room for BTC to co-exist with LTC.