So, I am all in favour of a locator challenge, even a country is helpful when checking matches and I try to see if i can add that to any potential unlocated match. However, I think the guidance needs more nuance.
Migration is a major factor as to why some profiles don't have estimated birth places, and so estimating a birth place from a marriage or child's place of birth is actually counter productive as it stops people picking this up.
The reason I raise this is because I have seen it in action. Someone recently, in trying to be helpful, added a death location of England to a couple of profiles I manage. I can see why, that's where they were born and several of their siblings lived their entire lives there. But, i can't trace these particular individuals in local records, so they definitely left the region and possibly the country.
I do think there are some rules of thumb that could work. For example, if their parents married and died in the same place, then there's a very good chance the child was born there. And to be honest, if someone married in England in the 1800s there was a good chance they were born there (unless they had migrated from Ireland), but if they married in somewhere like Australia, Canada or the US, then there's an equally good chance they were not.
I suspect this is the kind of thing you are thinking of anyway, but wanted to flag.
Thanks