You can already have your own clothes made for you, you can have your designs printed on T-Shirts or you can find a tailor, dressmaker or seamstress and have them custom make you something.

Companies like Nike and Adidas allow you to customize your own shoes.

But as for the future I would say it's pretty certain we will have 3D printers that can make clothes and then it will only be a matter of designing them on your computer and printing them out, companies are already 3D printing shoes so I doubt it will be long until that's available for the home user to also do. Or if the printers end up being industrial size things that are too expensive for the average home I'm sure someone will start a company that allows people to send in their designs and have them printed out.

For the moment it is cheaper for a company to use set methods for producing many of the same products and it costs them too much money to make small adjustments to the factory lines only to create one single unique item. But apart from that sooner or later robots will start replacing textile workers and the current machinery so that might change the structure of how clothes are manufactured from start to finish, giving the machines more flexibility and making it easier for one of a kind custom designs to be made.