Companies will take the easy & safe choices
Safe to them that is. Independent contractors will be deemed employed to avoid a tiny risk that they might get a fine. This is what happened 25 years ago when someone was not properly schedule D registered (ie self employed), the company who they had worked for had to stump up a tax bill. So companies/agencies/... then insisted that everyone work through a Ltd company. Something similar will happen now.
Doing a proper assessment takes time, so they will not bother as the time spent does not really benefit them.
I have a friend who does locum work for the NHS. She has classified by her current hospital as falling under IR35 & so employed (other hospitals classify the exact same position as outside of IR35); but does not get the benefits of employment such as holiday pay, sick benefit. She can now no longer claim hotel or travel expenses. The hospital pays the same, she has a large wage cut.
Yes: some were taking the piss, but many are not. We do need temporary workers for jobs that last a few months, often at a non-commutable distance from where the contractor has a home.
If the government wants more tax: go after the likes of Google, Facebook & Vodafone.