Presumably, in a complete Wikipedia, the percentage
would be much
lower (I believe the current estimates are that ~5% of all humans are
currently alive, and I'd guess our existing biographies are more about
alive people than that). But how does it compare to other
encyclopaedias?
That's a pretty irrelevant number. The %age of (known) notable people
alive today is much higher. How many people who lived over 1000 years
ago do we know enough about to write an article on (if we still know
about them, they're notable enough for me, so it's just a matter of
them still being known)? A few hundred, maybe? (most will be rulers of
the various countries that have records going back that far, I guess)
The number increases as we get nearer to present day, but the
proportion of living people that are notable is far higher than the
proportion of dead people that are notable (that we know of).