But certainly there are plenty of components (such as the plastic drive gears in a garage door opener) which can be printed and replaced by consumers.
And how often does the average consumer need to print out weird parts? (And how many of them actually have the skills, experience, and tools to make use of them?)
That is the fundamental limitation of 3D printing - the average consumer doesn't have significant need and/or the relevant skills. The "needs" 3D enthusiasts keep positing will enable the consumer (mass market) adoption are in fact edge cases.