On its most fundamental level, design is about fashioning something (vehicle) to deliver a benefit to a person (beneficiary). The more specific the benefit and person, the better a designer is able to tailor the vehicle to serve the beneficiary. Where the designer does not know much about his beneficiary or the benefit that is being sought, he can at best design a general-purpose vehicle that delivers a weak benefit to a broad audience, and at worst he will design a useless vehicle that delivers no benefit to anyone. And this is the problem of customization.
Before the advent of mass-production, personalization was the natural way of things. Each maker designed each object for a specific use by a specific person. Mass-production required compromise: to be efficient, a machine must make perfectly identical products regardless of the specific needs of the people who will buy them. And this was a compromise people were willing to accept for the sake of having goods available and affordable.
The next phase in evolution was a step backward toward personalization, but not quite achieving it perfectly: the notion of customization meant some combination of mass-production and personalization, generally favoring the former: mass-produced objects had the same basic qualities, but certain of these qualities could be altered to suit the needs or tastes of the individual customer. But the customizable features were defined by the maker, and the customization options were held to a very narrow range. This represents a better compromise, but is still a compromise.
And this compromise describes the present state of design, as it has for the past hundred years or so. The degree of customization varies by product and maker, but is still constrained to specific features and specific variations that the maker selects. Consumer satisfaction with this compromise seems to wax and wane: there is always the demand for products to be better suited to the needs of the customer, but an unwillingness to compromise on the price and immediacy of possession.
So in the present time, the majority of personalized products are only affordable to the wealthy, and the demand for personalization by the less affluent is both inconstant and inconsistent. There is some interest, but not the willingness to pay to achieve it. Makers attempt to better understand these demands, and are in some instances willing to serve them if there is sufficient interest that is supported by a willingness to pay and to wait.
For the most part, we remain stuck in the era of customization, flirting with the notion of personalization in a superficial way.