I thought that initially, but actually, the way it's worded, you need a family connection to actually play for the 2nd country.
I can see the situation that it deals with, the sort of situation where say a Tongan player gets a couple of starts for NZ, but doesn't really nail down a spot, they'e permanently excluded.
Looking at some other players who could benefit from this:
https://www.americasrugbynews.com/2019/09/09/foreign-born-raised-players-at-rwc-2019/
Jordi Murphy and Spain is another one that's actually potentially plausible.
I don't think it's a good rule, in many ways, I think it's compensating for the bad rule that is the residency one.