Yes, but isn't it the best option if people want to permanently transfer their coins to a different network?
Definitely
NOT!
This can't be done without any authorities. Which is (again) not an option for DEcentralized currency.
Minimal authority regulated option is to sell oldies/buy newbies. Did you ever seen shredded banknotes at currency exchange office?
How can you guarantee this transfer transaction? So much more when sending coins to unspendable address from currency-exchange (sometimes having 100+ input addresses in a single transaction)? Should this be named Proof-of-honour-word?