They will soon learn
The fact is that all of the skilled workers will go elsewhere and those that are willing to put in place a process to handle contractors outside IR35 (such as insisting they get a contract review and certificate) will have the very best contractors to choose from for projects. Those that put in a blanked PAYE or nothing will get the ones that are too stupid or unskilled to find another contract and so have no choice but to convert to PAYE. I think the banks will just end up with a bunch of mindless droids with all the real thinkers moving on.
I think they will soon wise up when projects start failing and they lose millions in income as they cannot keep up with the competition.
Next year will be interesting.