If you're talking about doing something in the future, do you say "somewhere down the road", or "sometime down the road"?
Interesting question! My first instinct is that both make sense, in different senses. "somewhere down the road" means to me something like "at some point along this metaphorical road that is the future." I think that's the way I would say it. But "some time down the road" makes sense too; I wouldn't be confused if I heard it. But my gut tells me it's less common.
This ngram seems to support that conclusion:
I think either one works just fine. As they would tell you on Physics.SE:
Distance = Rate × Time
Unless we are traveling by car, or giving directions, "the road" is probably not a physical road; and the phrase is being used as a metaphorical expression to mean "later" or "in the future". Since distance is a function of time, we get further down the road later in time, meaning somewhere and sometime are related to each other, and, in the context of this metaphor, virtually interchangeable. On this proverbial road, we can assume there are no breakdown lanes, so we always progress in location as we progress in time. Ergo, there's no set way to word it; for example, this works, too:
Solar preparation of new homes reduces the cost someplace down the road when that owner decides to buy a solar unit.
Moreover, there's one other alternative that hasn't been discussed, even though it is in use; namely, omit the somewhere/sometime/someplace altogether, and simply say down the road, as these authors did:
My fear was that, down the road, she would become dependent on others.
Climbing is not the direct source of happiness. Instead, it cultivates virtues that down the road will be a greater source of happiness.
One challenge is to convince the customer that, down the road, they will not exploit the position they enjoy as not only supplier of the product but also the sole source of changes, upgrades, updates, interoperability, and so on.
As to where or when that becomes bribery, it's a fine line. Especially when, down the road, there's a jury to convince.
One Ngram suggests that such wordings are not any less "valid" than using sometime or somewhere: