I could see unions making a big comeback in the US. They are still alive and well in the healthcare world (for nursing at least - my wife is a nurse at a large hospital in the US and has been a member of multiple nursing unions).

If you compare profit margins to wage increases there's an obvious (and expected via capitalism) disconnect. It's hard to galvanize this type of activity though. And new unions would definitely need a constitutional overhaul, probably based around transparency and making sure power and decision making is distributed.