It may be exactly like in construction. I help few friends with their tax returns (they work in construction). Situation is that although they're self employed (with all the bonuses and drawbacks of it) employer needs to pay their "expected" NI & PAYE taxes. So when they do their tax assessments those usually come with large returns due to expenses they can claim.
I have a feeling same will happen here - they will ask employer to pay your contributions directly to HMRC and people can claim them back if you provide all the proofs. People are not directly employed (they are still contractors) but are on payroll. System is really simple and already implemented. For PSC, where you're not supposed to muck with dividends and so, it makes sense.
It will just increase number of Ltd companies, which are more headache to manage. That will also increase workload on HMRC to analyse tax returns from those Ltds thus will be very counter-productive and expensive, IMHO.