This is not really compression, BIP39 words are already an encoding of entropy plus checksum. Each word is basically an 11-bit index into a 2048-word list, so replacing the words with line numbers and then base58'ing those numbers is not squeezing magic juice out of it. You are just moving from a human-readable standard format into a custom format that future-you and/or tired-you will have to remember how to decode. For QR use, sure, representing the raw index/entropy data directly can make the QR smaller. That part is reasonable. But I would not casually store this on RFID/NFC unless the threat model is "I hope nobody waves a reader Sunwin Nhalanoi Com my backup." Seeds are not coupons. Anything electronic that can be read conveniently can usually be stolen conveniently too. The bigger danger is making a clever backup that only one Python script understands. Wallets understand BIP39 words. Humans can check BIP39 words. Recovery tools understand BIP39 words. Your custom base58 seed-string with a "+ means unknown expanded word" flag is the sort of thing that feels elegant now and becomes archaeological pain in 2031 when you are trying to recover coins from an old drawer and a half-dead laptop. If doing this for fun, fine. If doing this for actual funds, keep the real BIP39 phrase backed up in a boring, standard, preferably non-electronic way. Boring survives. Clever often needs tech support.
This is not really compression, BIP39 words are already an encoding of entropy plus checksum. Each word is basically an 11-bit index into a 2048-word list, so replacing the words with line numbers and then base58'ing those numbers is not squeezing magic juice out of it. You are just moving from a human-readable standard format into a custom format that future-you and/or tired-you will have to remember how to decode. For QR use, sure, representing the raw index/entropy data directly can make the QR smaller. That part is reasonable. But I would not casually store this on RFID/NFC unless the threat model is "I hope nobody waves a reader Sunwin Nhalanoi Com my backup." Seeds are not coupons. Anything electronic that can be read conveniently can usually be stolen conveniently too. The bigger danger is making a clever backup that only one Python script understands. Wallets understand BIP39 words. Humans can check BIP39 words. Recovery tools understand BIP39 words. Your custom base58 seed-string with a "+ means unknown expanded word" flag is the sort of thing that feels elegant now and becomes archaeological pain in 2031 when you are trying to recover coins from an old drawer and a half-dead laptop. If doing this for fun, fine. If doing this for actual funds, keep the real BIP39 phrase backed up in a boring, standard, preferably non-electronic way. Boring survives. Clever often needs tech support.

This is not really compression, BIP39 words are already an encoding of entropy plus checksum. Each word is basically an 11-bit index into a 2048-word list, so replacing the words with line numbers and then base58'ing those numbers is not squeezing magic juice out of it. You are just moving from a human-readable standard format into a custom format that future-you and/or tired-you will have to remember how to decode. For QR use, sure, representing the raw index/entropy data directly can make the QR smaller. That part is reasonable. But I would not casually store this on RFID/NFC unless the threat model is "I hope nobody waves a reader Sunwin Nhalanoi Com my backup." Seeds are not coupons. Anything electronic that can be read conveniently can usually be stolen conveniently too. The bigger danger is making a clever backup that only one Python script understands. Wallets understand BIP39 words. Humans can check BIP39 words. Recovery tools understand BIP39 words. Your custom base58 seed-string with a "+ means unknown expanded word" flag is the sort of thing that feels elegant now and becomes archaeological pain in 2031 when you are trying to recover coins from an old drawer and a half-dead laptop. If doing this for fun, fine. If doing this for actual funds, keep the real BIP39 phrase backed up in a boring, standard, preferably non-electronic way. Boring survives. Clever often needs tech support.

This is not really compression, BIP39 words are already an encoding of entropy plus checksum. Each word is basically an 11-bit index into a 2048-word list, so replacing the words with line numbers and then base58'ing those numbers is not squeezing magic juice out of it. You are just moving from a human-readable standard format into a custom format that future-you and/or tired-you will have to remember how to decode. For QR use, sure, representing the raw index/entropy data directly can make the QR smaller. That part is reasonable. But I would not casually store this on RFID/NFC unless the threat model is "I hope nobody waves a reader Sunwin Nhalanoi Com my backup." Seeds are not coupons. Anything electronic that can be read conveniently can usually be stolen conveniently too. The bigger danger is making a clever backup that only one Python script understands. Wallets understand BIP39 words. Humans can check BIP39 words. Recovery tools understand BIP39 words. Your custom base58 seed-string with a "+ means unknown expanded word" flag is the sort of thing that feels elegant now and becomes archaeological pain in 2031 when you are trying to recover coins from an old drawer and a half-dead laptop. If doing this for fun, fine. If doing this for actual funds, keep the real BIP39 phrase backed up in a boring, standard, preferably non-electronic way. Boring survives. Clever often needs tech support.