1a) My son will become a college student next year.
1b) My son will become a college student in the next year.
1c) My son will become a college student the coming year.
1d) My son will become a college student in the coming year.
Within this group, I don't like (c), and would suggest that a student change/correct it. The others are fine, but the nuance differs.
In (a), the listener might expect/conclude that it will happen at the typical time (April here, Sept. in the US).
(b) and (d) seem to have the feeling of "sometime in the next/coming year," but exactly when is more uncertain. In these, "in" is comparable in meaning to "during".
With the right stress, these three could also be used in contrast to answer the question: "Your son started college this year?"
Again, this is nuance, or possibility,