When I started working in GIS 30 years ago, the possibilities where not that many and not too many fields of education were using GIS. Areas using GIS were natural resources, environmental science, agriculture, universities (education and research), archaeologist, engineers (most people moving from CAD) and a few others. These days, I say, “GIS is everywhere!” and you can apply GIS to almost any area. Think about any career and there is a good possibility that GIS can be implemented.
GIS as a career is a great option but knowing how to use GIS in your career makes you more marketable and appealing to a potential employer.
With the new applications to so many areas, the only way I see GIS is to keep growing during the next 5 years... and during the next 10 years as well.