Doesn't matter; software changes rapidly and you shouldn't get married to any one implementation (or stock in a promising new sector).
By all means, upgrade the protocol, even to the Litecoin or Monero protocol or whatever. But to change
ledgers every time you need to upgrade the protocol doesn't make sense at all. People don't want to have to play stock trader with their bank account.
Fortunately, because of spinoffs (and maybe sidechains), the Bitcoin ledger is a safe place to store value even if the Bitcoin
protocol gets superseded.