I have never really understood the advantage of Shamirs Secret Sharing over multisig.
I see that Shamir's secret Sharing only as an alternative to passwords, not as an alternative to multiwallets. So in most cases this feature is not needed at all. Here are two examples:
Scenario #1: Multiwallet 2-of-2, passwordless
With BIP39 you can use two keys, e.g.
before circle champion auto sleep embody nose february illegal refuse solve build
and a second key:
enable struggle rather mail sea ski similar achieve ride wave hold black
The equivalent version with my proposal would be to use two 1-of-1 keys, e.g.
banof gubit zokom zimuv tahuz vohih sahir nanuv vibar
and a second key:
babor josas zasag dotit sasub jinug fanim lazup zogiv
The advantage of using my proposed proquints encoding here is that it's language agnostic, shorter, and provides better safety against typos
Scenario #2: 2-of-2 Multiwallet, one part password protected.
Again say you want to have a 2-of-2 multiwallet. In BIP39 it looks like this:
Part 1:
dentist liquid evoke universe clinic convince cute erase fold about swap anger
Part 2:
pepper cliff fruit wise extend daughter symptom quick once love shadow snap
password for part 2:
my secret password that I will surely remember
In my proposal Part 1 is equivalent to above, a simple 1-of-1 proquint encoded key:
bakad pusuz mamis vinod vutat siniz jutur vunun ruluv
For the second part of the multiwallet, since I do not support passwords, the alternative is to use a 2-of-2 shamir's secret:
batuh nifat sizip jimuz hiror hibus masum ragis guhid
bijol guhuh rudis hijag jofir virif duruv hudoz kufis
So instead of the 2 parts mnemonic & password, the key consists of 2 parts mnemonic & mnemonic. The main advantage here is that the password is replaced with another share that is required to reconstruct the secret.