What are the best practices and tools to increase security of the mnemonic/seed phrase? For example I can imagine building a deterministic permutation in order to create a trapdoor mnemonic. Same could be done by using non-standard derivation path.

Full-time builder. Pimlico | @33bits | farcaster-solidity. Zero-knowledge and asynchronous transactions evangelist.

The Art of Exchange, The Science of Payments

Co-founder, Cosmos. CEO, Informal Systems. 

Exactly, that's what I was looking for! And what is the state of modern wallet support? I've seen an option to enter a passphrase in Ledger/MetaMask/Coinbase wallet/etc.

Working on building products with zkTLS. A ruthless empiricist.

http://opacity.network

Advisor @ EV3 Ventures

This or any similar solutions

https://warpcast.com/buchmanster/0x44ea2710

I’m not following what your goal is, can you give more detail on what you’re trying to achieve?