I wasn't asking Electrum to support Lightning on either old wallets, or even old addresses in any wallet (old or new).

The new wallet I spoke about in my example wizard-creation timeline would be a completely new wallet, created in the normal way.

I accept the master public key would change due to the new seed... but we can already export/import labels now.  So presumably if we can import the old wallets addresses (at least those that have had at least 1 or more transactions) then the import would line up with those old transactions.  **Then** enable LabelSync and force an upload.

Is there any reason Electrum doesn't support importing private keys of old addresses from a previous wallet?  I get that there might be the temptation to stop this from happening (in case someone does something stupid and tries to carry on using them), but if we mark them as 'defunct' or something then it should hopefully stop or at least deter someone from using them going forwards... but at least everything is under the one re-made wallet.