It has already happened. Philips has designated 3x months for a single toothbrush lifespan, which may or may not be the case (depending on one's toothbrush using habits) as the head clearly does not annihilate automagically after three months. For the sake of the conversation, let's say the recommendation is valid.
Where it gets more interesting, though, is actually not at Philips but at shops that sell replacement heads. Sale assistants do go out of their way to actually lie to their customers and tell them that a single toothbrush head will last, like, many-many-many months. And when asked at the next shop visit about why the toothbrush started yelling three months after replacing it, they will blink their eyes and literally inform the customer of «having never heard before about it from any other customers». The situation happens on a regular basis, and the only recourse that works with such people is brushing the pesky flies aside and politely ignoring them. Since not every customer can or does that, the ink business of electric toothbrush replacement heads prospers.
Where it gets more interesting, though, is actually not at Philips but at shops that sell replacement heads. Sale assistants do go out of their way to actually lie to their customers and tell them that a single toothbrush head will last, like, many-many-many months. And when asked at the next shop visit about why the toothbrush started yelling three months after replacing it, they will blink their eyes and literally inform the customer of «having never heard before about it from any other customers». The situation happens on a regular basis, and the only recourse that works with such people is brushing the pesky flies aside and politely ignoring them. Since not every customer can or does that, the ink business of electric toothbrush replacement heads prospers.