I’m of the opinion that it’s unlikely to happen within 50 years.
But I still think it’s a good idea to start switching over to post-quantum encryption, because the lead time is so high. It could easily take a full 10 years to fully implement the transition and we don’t want to be scrambling to start after Q-day.
Moving from SHA-1 to SHA-2 took ~20 years - and that's the "happy path", because SHA-2 is a drop-in replacement.
The post-quantum transition is more complex: keys and signatures are larger; KEM is a cryptographic primitive with a different interface; stateful signature algorithms require special treatment for state handling. It can easily take more than 20 years.
But I still think it’s a good idea to start switching over to post-quantum encryption, because the lead time is so high. It could easily take a full 10 years to fully implement the transition and we don’t want to be scrambling to start after Q-day.