Keystone should add an ability to Shamir backup using 20 words. 20 words offer 128 bits of security, which is more than enough for long-term storage. The reason why 256 bits (24 words with normal mnemonic) were used, is because people were splitting the words into insecure shares (3 shares 1.-12. word, 13.-24. word, 7.-18. word). Now with Shamir Backup that's not needed anymore (you just create more shares), so you should offer 20 words. In addition, your supplied cards don't offer more than 24 words anyway. It is also extremely time-consuming to do 33 words of writing + checking, especially if the device shuts down on you in the meantime, and you have to reset the process (which happened to me).
Keystone should add an ability to Shamir backup using 20 words. 20 words offer 128 bits of security, which is more than enough for long-term storage. The reason why 256 bits (24 words with normal mnemonic) were used, is because people were splitting the words into insecure shares (3 shares 1.-12. word, 13.-24. word, 7.-18. word). Now with Shamir Backup that's not needed anymore (you just create more shares), so you should offer 20 words. In addition, your supplied cards don't offer more than 24 words anyway. It is also extremely time-consuming to do 33 words of writing + checking, especially if the device shuts down on you in the meantime, and you have to reset the process (which happened to me).