If I buy a Trezor or a Ledger, I will have to start another wallet and send all my sats to there, right?
Discussion
Obviously!
Waiting for delete button on Nostr 
NIP-09 is implemented in many clients like amethyst already.
If you want to gain the security associated with a seed that has never been entered somewhere else than on the secure signing device of your choice, then yes. If you don't care and keep this for the wallet you've been using in mind, then no.