If you generated your seed with Trezor, there is no need to worry about Electrum. Your seed isn't supposed to be imported into Electrum. You only connect the two to use Electrum as the interface instead of the Trezor Suite. Your keys remain on the hardware wallet. On the other hand, if you are planning on using Electrum as a cold wallet, then there is no need to include your Trezor in that setup. You sign the transactions on your airgapped device and broadcast them on an internet-connected computer.
But why do you want to import your cold wallet to an online wallet, all what you need I just to create a watch only wallet by importing your master public key to the electrum wallet.
It wouldn't be an online wallet the way it was explained in the OP. He would use Electrum as a cold wallet.
Am I correct in thinking that Trezor wallet will be fully future compatible with electrum wallet if I create the 12 word seed and passphrase in electrum wallet and use it in Trezor. I would do this air gapped.