"Soon" can often replace "in the near future," but not always. That is because the meaning of "near future," and therefore other ways to express the same idea, depends on context. "Near future" for the opening of a new railway line is further away than "near future" for having one's hair styled.
"In the near future" is often used to avoid having to specify a timeframe, especially if you don't wish to commit to doing something by a certain due date and then be held responsible for achieving this.
Unfortunately, you cannot use "soon" to ask a question about someone's plans.
You'll probably need to be more specific in terms of timeframe. So you could ask, "what are you planning to do over the next few months/weeks"?
If you want to know about their plans within a shorter timeframe you can ask, "what are you planning to do next month?"
You can also ask, "what are your plans for the next few weeks/months?" This latter example is more of a casual, friendly enquiry.