What if sex work were somehow redesigned to exclude the most exploitative jobs in the industry?

I don't think that these jobs can be somehow excised from the sex industry as a whole. They are in fact an integral part of the sex industry which must exist as the bargain lower-end piece of any industry in a capitalist society.

What I mean by this is that every object we buy, from plumbing equipment to tube tops, has an expensive, "nicer" version that people tend to prefer and pay more money for, as well as a cheaper one. This is just how consumption goes. The problem is that if you turn people, like sex workers, into consumable objects, you are necessarily going to have the cheaper, less desired, minority, no-protection-required, "ugly" version for the cheapskate hobbyist as well as the supermodel regularly-tested escort who services CEOs and politicians.

If union-busting and ineffective unions exist in other industries, they would exist in the sex industry too. If human rights violations can still take place in the treatment of legal unionized factory workers, they would still take place in the treatment of sex workers. This is not an acceptable risk for either factory workers or sex workers.

If you can pay someone who looks just like a celebrity two thousand dollars for a night in a fancy hotel which includes a nice dinner and a bubble bath, you will necessarily also be able to pay someone else twenty dollars for unprotected anal sex, punch them in the face, and run away before they realize you only gave them fifteen.