• When you create a software key it gives you the seed like any normal wallet. 
• If you are using a Coldcard then it’s just the Coldcard seed, there isn’t a new one for the wallet.
• If it’s multisig you need to also save a copy of the wallet config. I always simply email that to myself, it’s needed to restore, but isn’t terribly sensitive, I prioritize availability over privacy there. Although I send from a protonmail account to another protonmail account with the subject “BACKUP” so it’s just always searchable in email if I need it.

There is nothing uniquely different about Nunchuk and key backups. It forces you to save your seed during the key creation process like any of them. You might be remembering incorrectly or confusing how you set it up? 

 it does NOT force you to backup the seed for a key created as part of a hot wallet initialization. 

 Correct. There’s nothing Nunchuk does uniquely regarding backups. You can use Nunchuk with other hardware signing devices (for which seed generation/backup should be handled separately on the hardware), or you can use a Software key, which Nunchuk generates and gives you the seed phrase for.

The scenario the OP mentioned specifically has to do with an edge case where user created a hot wallet (with a hot key that you can back up later), then CHANGED THEIR MIND and delete the hot key AND REUSE THE SAME HOT KEY (that user hasn’t backed up) in a multisig wallet. This might warrant a fix, but not how the majority of people use Nunchuk. 

 *Correction: delete the hot wallet 

 The fix is fairly simple: expose the seed export option within the Key Info of the hot key, even if the hot wallet has been deleted (and user hasn’t viewed the seed yet).