The legislation requiring IR35 status to be determined by private sector companies is contained in the 2019/20 Finance Act, which is still in draft. It would normally be presented with the Budget and voted on by Parliament, which is currently done in October.
Now, the Government, having prorogued Parliament, cannot have a Budget while Parliament is not sitting, and when it does sit again, will be very busy preparing for [Brexit][Election][Further Prorogation][staying out of prison]*, so are unlikely to have a Budget at any time soon.
Even if they did, and they remained in office long enough, the way the numbers stack up it would seem very unlikely that they would get the Budget to pass.
AIUI, the emergency financial statement that the Chancellor presented earlier in the month was enough to allow the tax rates and some other financial instruments to roll over in April (they are also normally presented in the Budget), but they did not pass this years Finance Act in it's entirety into law.
So, if we accept that normal government will not resume until things have settled down one way or another, I would say that it is exceptionally unlikely that we will get any sort of Budget until the new year. This make the cries of there being not enough time to implement the IR35 changes even more poignant, and that makes it likely, IMHO, that the measures will be delayed until at least April 2021.
*Select any/all appropriate choices
P.S. I am not am accountant/lawyer, so this is just my thoughts on the matter. It does not directly affect me anyway, I work through an Umbrella!