Is it permissible to perform Istikhara regarding future plans that are not detailed, such as someone performing Istikhara to become a writer within four years?

The Istikharah prayer is prescribed for future, planned matters. Its time is when one intends to do or abandon something. So, if a person has made a plan for a matter and intends to act upon it, Istikharah is prescribed for him. However, mere contemplation without a firm intention to act does not warrant it.