It's true that with the one assembly line taking care of all global orders, if the early adopters from all the targetted markets put in an early order then we'll all be looking at a long waiting list. I'd imagine the time for pushing an RS through the line to be longer than for the standard car, but maybe this is outdated thinking.
It's interesting because there's good and potentially bad aspects to a centralized global production. On the plus side, they will have all the experience from building the regular focus, and as soon as there is a problem, they can quickly integrate the fix into the production line. All the quality control can be focussed on the one production line for the RS, but at the same time if there are issues that are known to affect the regular and ST versions, the RS line will be able to take those into account as they fine-tune the production process.
On the negative side, it might take a while for the designers and engineers to get their hands on feedback from customers in other parts of the world. Let's say the american drivers identify one fault, and the japanese users identify another, then the information has to be channeled through, interpreted, and any changes need to be validated to conform to the norms of all those places. That could be a problem actually. I imagine they have a list of requirements for conformity at a global level, but to develop solutions and integrate them into the already-running production line while at the same time making sure it works everywhere in the world is quite a tough job.