I know they are using different BIP formats but ledger should accept other BIPs for importing seeds and not just BIP39, and derivation path may also be issue sometimes.
Electrum seed phrases are not a BIP at all. They use their own system as detailed here:
https://electrum.readthedocs.io/en/latest/seedphrase.html?highlight=seedI need to check with ledger documentation for more info, and I wonder can Electrum seed words be imported to any wallet other than Electrum?
You can use Electrum as an interface to your Ledger Nano hardware wallet, but in that case the wallet is being derived using the BIP39 standard from the seed phrase created by your Ledger device. You cannot import an Electrum seed phrase to a Ledger device. As far as I am aware, Blue Wallet is the only other wallet which accepts Electrum seed phrases.
Imagine if one day electrum doesn't exist anymore their servers are down and you are stuck with their unique seed words format...
Not really a concern. As long as you have any old copy of Electrum, you can insert your seed phrase, recover your wallet, and then extract your private keys for use in another wallet, regardless of whether Electrum has been discontinued and there are no Electrum servers. The differences between turning an Electrum seed phrase and a BIP39 seed phrase in to the associated wallets are also very minor. You can edit a version of iancoleman to work with Electrum seed phrases by making two very small changes. It will always be possible to recover from Electrum seed phrases.
Rath_ talked more about this:
You can't import your Electrum seed anywhere because it differs a bit from BIP 39 seeds (
see this). You could get your Master Private Key and import it into a wallet which supports such a feature. If you want to have the same wallet in both Electrum and Wasabi then you should use Wasabi to generate a BIP 39 seed and import it into Electrum. You cannot convert your existing Electrum seed into a BIP 39 compatible one.
You have to be aware that Electrum seed phrase wallets derive at different paths to BIP39 seed phrase wallets, so if you export your Electrum seed phrase master private key to import in to another wallet, you will need to be able to specify the necessary derivation path. m for Legacy and m/0' for Segwit, as opposed to the more familiar m/44'/0'/0'.
So I can export private key, but I don't think that importing private keys is possible for hardware wallets, correct me if I am wrong.
This is correct, as again, importing an externally created private key completely negates the point of the hardware wallet in the first place.