Tools to improve speed of development have existed for ages, twice the speed = twice less developers in a blunt way. (that includes even programming languages)
Personally I'd consider it an improvement - if I job can be automated, it should be.
Except that's not how that works. Increasing the productivity of a job does not eliminate it. A job is eliminated when it's no longer necessary.
Unless you live in a parallel dimension, we're both in the world where there's more and more software development being done every day. Twice the speed results in twice the output, not half the developers.
Of course it does. Not on an individual level, but if suddenly one employee can do three times more work, there is no need to recruit 2 more full time jobs to address the increasing needs. So on the whole, productivity will destroy jobs, but the good news is that the additional returns will create other jobs in other areas.
In some cases, if productivity increases, and the price performance follows, we will consume far more of a thing, growing the market and employing more people.
None of the advances in software development have eliminated software development. Hell, there are still job openings for COBOL developers. CI hasn't resulted in a whole swaths of people suddenly out of work because they were running tests by hand and now there's nothing else they can do.
Now, extend that to salaried positions. There is a certain amount of work that must happen. Tooling improves, devs become more idle, management consultant fires one (over time).
This has been somewhat negated only because the role of computers has been growing quickly and outpacing the growth in efficiency. That will change at some point. As you said, there won't be a case where swathes of people are suddenly out of work, it will be gradual.
A guy I know is an economist and does consulting for factories to optimize production. He has talked about how some areas these days have removed large groups of humans and replaced them with single humans observing machines. Eventually, development could reach a similar place.
If manufacturing cigarettes gets more/less expensive, people will pay more/less for their cigarettes. If it takes fewer people to make cigarettes, fewer people will have jobs making cigarettes. The number of cigarettes smoked stays constant.
If you have more lawyers, you'll have more lawsuits, contracts and legal letters. If it gets easier to do contracts or lawsuits lawyers will take longer lunches. Lawyer fees stay constant.
I think you mean half fewer developers, not “twice less”, but...
No, twice the speed means twice the value produced per unit labor, which means at the same labor price level, more, not fewer, programmers will be hired (or, at constant employment level, pay should increase); the actual result is some increase in pay and some increase in employment.
Technology that provides output multipliers on a job are different than technology that replaces the function of workers at lower cost.
But what if it's not ?