People won't like to talk about it but quantum computing would soon be a threat to bitcoin. A study suggest within 15 to 20 years, the quantum computer would be strong enough to guess a private key with balance in 7 days. A problem with quantum computing is running them is still much expensive and in control of large companies or government. But wait 30 to 50 years and quantum computing would be in hand of every enthusiast.
It's sad but the life of bitcoin as such is a 50 years max. There's no point in making bitcoin time capsules for your grand child. And no, small modifications on bitcoin won't make it survive. It's not just bitcoin but almost all of cryptocurrencies would suffer. But it would also bring in new encryption technologies which would be far superior.