I don't really know about this, but rest assured that I won't let foreign workers pass unnoticed
I had a few minutes yesterday night to look at the game, and I wanted to check our settler factories.
Karakorum looks ok as soon as we have mined the two bonus hills and a grassland, using 3 irrigated FP as well to reach +5 fpt.
Shields should be ok with the extra ones coming from the forest upon pop growth (if I am correct, it was getting late at night and my brain has tends to stop working without advance warning...).
The situation in Kazan looks a bit more complicated, at least at a first glance.
It seems a bit short of shields, so all I can easily see is a two-turns workers factory at size 5 (with granary): irrigated FP+wheat will give the +5 food per turn we need. Then two pairs of irrigated FP + Forest will bring the spt to a total of 5 (1 comes from the city centre).
I could not find a way to turn it into a fast settler factory as it is -what I saw, on the other hand, is that if we moved Kazan 1 tile West, it would have access to:
Irrigated Wheat on FP: +3 fpt, 0 spt
Irrigated Sheep on Plains: +2 fpt, 2 spt
Forest: -1 fpt, 2 spt
At size 4, add an irrigated plains for +5 fpt, 6 spt
At size 5, add another one for +5 fpt, 7 spt
At size 6, add yet another one for +5 fpt, 8 spt (would neet at least a forest chop).
So another 4-turns settler factory seems feasible in this case, either between pop 4 and pop 6 (with a similar mechanism to the previous case) or between 5 and 7.
I am not sure this is correct either: anyone cares to cross-check?