IR35 has put paid to quite a lot of your suggestions for hourly/daily workers using companies to avoid tax.I read that and was a bit baffled by it really. I would've thought the greater revenue would come from people whacking their pay into pensions and company cars to reduce their pay to under £100k, especially if they are people who currently benefit from the tax-free childcare which drops off a cliff at £100k. We must lose a significant amount of tax over that.
I don't think many people are avoiding working more hours to avoid the £100k trap; in fact I'm not sure there's that many people working hourly on that kind of gross income, and if they are they're likely invoicing hourly from a limited company and would have other ways of avoiding it anyway, like expensing their commute travel and lunches or giving themselves trivial gifts or maxing the annual social functions allowance, or even having their partner on as a shareholder. So of course the OBR's conclusion is that it wouldn't raise enough revenue via working extra hours.
The groups you are missing are doctors and various other professionals who are able to cut down to a 4 or 4.5 day week. In the case of doctors they also have the ability to work hourly overtime, and the structure of their pensions makes it quite difficult to even use that as a way to avoid the trap.
I don't have access to the data of course, but it seems entirely believable to me that you could increase tax take by removing the trap. There's a lot of highly trained experienced people starting to reach that ceiling, and if they all realise that they're better off working less and having free time then we're in some significant trouble.