As I suggested, basically, at the end of the day, you have to give the workers a future, something to look for. Assuming they work for five years, if they know they can apply as landed immigrants, that would be different. Now they are only under the working permit. They don't know what will happen a year or two down the road. That's why you give employers a chance to abuse the system too. If they knew that definitely, after three or five years, they could apply as landed immigrants, that would be a different story.
So that would be number one: if they abide by all the laws, they can apply as landed immigrants. Number two, regarding changing employers or whatever, that's not a big issue at all. I've come across a few Chinese who are undocumented workers. If they knew....
Well, I'll put it this way: I'm sorry to say that those guys abuse the system. I say that because they know they'll never be able to get permanent resident status. The only way is for them to go through a phony marriage. After you apply for marriage, you can get a working permit and can start working--start working properly, as in you don't need to be paid cash and so forth. They can apply for a social insurance number, work for regular pay, or whatever.
Basically, at the end of the day, for all of those undocumented workers or foreign workers, you have to give them a future, something to look for.