I think the selectivity problem is less of one for programmers than screen actors. We can use code tests or Github for membership screening. Thus, we don't create the chicken-egg problem where (a) it's almost impossible to prove yourself if you're not part of the union while (b) you have to prove yourself before you can join.
Getting broad-based membership is much harder. This is an industry full of (a) young people who think they'll have investor contact in 6 months and be founders in two years and retired in six, and (b) indentured servants on H1-Bs. Even if we get 95% of the top 50% of programmers (and that's wildly optimistic) as members, most managers will just ignore their need for talent, in that case, and hire bottom-rung engineers, preferring that over being responsible for bringing in a union. It (that is, hiring bad engineers to avoid bringing in represented ones) won't work, but it won't hurt those managers' careers personally, so nothing will be done about it.
Getting broad-based membership is much harder. This is an industry full of (a) young people who think they'll have investor contact in 6 months and be founders in two years and retired in six, and (b) indentured servants on H1-Bs. Even if we get 95% of the top 50% of programmers (and that's wildly optimistic) as members, most managers will just ignore their need for talent, in that case, and hire bottom-rung engineers, preferring that over being responsible for bringing in a union. It (that is, hiring bad engineers to avoid bringing in represented ones) won't work, but it won't hurt those managers' careers personally, so nothing will be done about it.