Making something like a Nxt Electrum could be very beneficial, but it would be much more complicated than building a Bitcoin/Litecoin version.
I disagree. NXT already uses a brain wallet concept. You could think of that as the seed if you want.
So, My NXT Lite wallet could take two approaches, I could decide or leave it up to the user:
1. The user remembers his passphrase/seed and nothing is stored for him. Since this is a "light wallet" it will remember your ID(s) and can display your balances/assets etc by only knowing your ID. You could even "add" an address without every giving the wallet the password/seed.
2. It could work like a bitcoin wallet. Where it creates a wallet.dat file to store your passphrases and encrypt that wallet file using a password/pin your provide. Either the wallet can generate a password/key for you or you can provide (import) an existing wallet.
Nothing complicated about it. It looks/feels the same to the end user as the current Electrum if that is what people wanted. The software could even be deterministic, it could generate a seed, and then use that seed to generate additional accounts if you wanted more than one. So, you could recover a whole bunch of IDs with a single seed.