Like I said, product launches are very complex. It doesn't work the way you think it does. You don't lock things down well ahead of time and then launch them. You have a project timeline with a lot of moving pieces and there's usually a mad dash to the finish line.
Someone was clearly confident that part of the tech could be completed in time so Tim announced it on stage. It didn't work out that way. It happens. They're human too.
Steve Jobs announced a white iPhone that took a year to finally hit the streets. And that's just paint! Admittedly, a pristine white is the hardest color to produce but it goes to show you not everything always goes according to plan... sometimes even the simplest things can trip you up.
The white iPhone color option was NOT essential to the core functionality of the iPhone. They didn't start with the idea of a white iPhone and fill it with the rest of the technology. They designed the phone and decided to offer white likely late into the process, and discovered it wasn't as simple as they expected.
In this case, the ability for the two buds to stay in sync is critical to the functionality of the device. If the prototype couldn't at least do that, they didn't have a product.
What you're suggesting is like a car maker designing an engine for a car that doesn't work properly and decide to keep building the car it will power, and introduce it, even though the engine doesn't work, hoping it will all work out before the have to start delivering them in massive scale. Add to that the new car is critical to the success of the car maker, just as the AirPods are to the removal of the headphone jack.
If this rumor is true, then it's absolutely stupid that they didn't get the synch problem solved before they introduced them. If it's something else, as you seem to be suggesting -- like a part not being ready for mass production; then that's a different issue. I'm commenting on the rumor.