I fail to see how that's going to be useful since not only will it have the same effect of generating more addresses inside a single wallet, but there will also be more mnemonics to write down.
If the given wallet is BIP85 compliant then there is no need to write down all child mnemonics. All of them are derived from a single master SEED which makes mnemonic management to be very easy matter. For instance in the case of HW backup one has to write down solely the master mnemonic and be safe forever. BTW, Passport 2 has such functionality as generate multiple child SEEDs from master mnemonic.