There would be too many farm teams if you were allowed to create a second team in the same country. Imagine the Chinese U21 and NT...
Not concerned about farm teams to be honest. Mainly because I wouldn't mind seeing a few farm teams here! And it may have the result of leveling up the competition, considering I expect China already has farm teams, whereas we really don't.
China already has a number of farm teams and it makes them the best, most other countries probably have one or two. While allowing a second team would also allow the chinese to have more farm teams I think they already get most of their best talent so would see only a marginal increase whereas Australia would see a significant jump in its talent level.
For example, imagine if 10 Aus managers had a second team purely as a farm team. They have saved money over a number of seasons and have 1.5 mil each. This season 5 of them buy stud 18yo's, next season the other 5 do the same, and this is on top of the other draftees who are kept by their managers. Imagine the depth well organised countries would now have.