If you are going to create true entropy, such as you would by rolling dice, and then commit it to memory, then why not just generate a seed phrase in the usual way and commit that to memory?

Memorising your wallet/seed phrase/brainwallet input/whatever is universally a bad idea due to how fragile human memory is, but at least if you memorize a seed phrase your coins won't be stolen almost immediately as they would be with the vast majority of human generated brainwallets.