Hi josh, I didn’t look into the details of how the recursive secret splitting works, but it seems reasonable and it’s very cool that this can be done at all. Good work!
In a way, it could be considered a generalization of the scheme: in the form I proposed, the "parties that can decode the backup are (a subset of) the parties providing the xpubs, while with your scheme you can also enable thresholds of them, and more complex subsets matching (some of) the spending conditions defined by the miniscript rules.
In practice, I still expect that the simple choice is the best for most users, and likely has a much lower adoption barrier because of the much simpler implementation complexity. In particular, if recovering from backup requires multiple parties, building a UX for it is substantially more complex in a wallet.