One of the importance of seed phrase is the ease to back one’s wallets without having to store the master private key or any key at all. I get where you’re concerned about, like electrum not been in existence again, currently there is a BlueWallet that is said to support the custom seed phrase from electrum wallet.

But aside that should they stop to build/develop the wallet again, another developer could easily build it up since its source codes are open.

But also if at a time there is no wallet that supports the seed phrase, you can still generate the master private key from the seed phrase using tools because the method it uses to generate its seed is not that different from the Bip39 seed phrase. So there is nothing to worry about