I believe it’s time for more complicated city management. Rather than having one race for each city. Multiple races could migrate to a city. Having multiple races in a city should give many more options but control would be much harder as the unrest should raise via, terrain features or else.
I already play some games with that option, and city population growth like other, but when population get +1, the generated race is cyclically chosen by races present in city (in planet, it was on ES2).
I do not really like this.
In my opinion, a good manner to manage a multi racial population cities should be to consider that you have several cities superimposed in the same territory, one per race.
Example : A city with 10 dwarves and 2 humans : consider this like a city with 10 dwarves and another city with 2 humans, each one with its own growth system.
Some ressource can be used only by few races, or shared by some races.
Ex: Food, if races eat same food, but you can also have a race who eat something else, another ressource... in fantasy you can have a race who eat pebbles...
____You could have racist politic who give ressource priority to a race from an other, or not...
Ex: Religion building, can be shared if races share the same religion, but also is only usefull and built for/by race who follow that religion, not by others.
____In a "multi superimposed cities system", in your citiy you could build several building simultaneously, one per race, but also a race can help to build something for an other race... perhaps this could depends on relationship between races
This race agree to do this with the other race ?
This race understand how to help the other ? the understanding between races can growth other time if they coexist, some race can have affinities each other, others don't.
And for population growth... you could see some new population that appear because of mixed races
Ex : A citiy with elf and humans, you will be half-elf who could appear in your population after some time... a 3th race ?
It is a new system to invent !
And like you, i hope that a good system will be developped... it's time for this, like you said.