Loose Rivet Today the decision making element does not need to be certified.
If the umpteenth next generation was to be what I called autonomous, the software "AI" would need to be formally reviewed and approved.
Through that the development cost will be enormous and unpredictable as well. Not to make a code that works, but a code that you can prove won't do anything else apart from what it says on the tin.
My take is that the investors would not approve a launch of a project where the worst case cost are impossible to estimate.
You can pretty y much always fix and aeroplane but code sometimes just cannot be. And a replacement one is prone to another full set of unknown bugs, just like the original one.