I had to explain the purpose of an umbrella company to a client in the US recently. Perhaps that structure will become the standard way for contractors to work over there too.
The biggest risk for this is people who "really are" independent but are currently working on a long-term contract for a company, and it sounds like we'll have to wait for case-law to apply.
I suspect the rule of thumb of "you make $50/hr or more effective" will probably continue to hold.
The employer is legally liable for lost tax revenue if they fail to determine status correctly.
The result: most employers decided that contractors were inside (treated like an employee for tax purposes with none of the benefits of employment) rather than risk getting it wrong.