Well they can ask.....
As there is no real definition of what is a city and what the limits of each city are I'm not sure they will get a useful answer. The population of the "City of London" (Q23311), for instance, is only 7,375! Should we change it from 'instance of:city' to 'instance of:village'?
Even a basic query like 'people born in the Czech republic' has problems. Should it include people born in Czechoslovakia or the Austro-Hungarian provinces of Bohemia and Moravia? To exclude these the query needs to check not just if the 'place of birth' of an item is 'in the administrative entity:Czech Republic' today but whether that was true on the 'date of birth' of each of those people.
This isn't to say that such queries are not useful. Just to point out that real world data is tricky. The cool thing is that we are going to have the data in Wikidata to make it theoretically feasible to drill down and get answers to these tricky questions. Once the data is there, open licensed for anyone to use, then it is just a matter of a letting loose a thousand PhDs to devise clever ways to query it.
If we build it they will come!
At least that is my understanding.
Joe