I'm learning WordPress and I'm enjoying developing sites. However the entrepreneur in me is wondering what other services would be in demand besides building sites. Maybe areas such as securing Wordpress sites?
Wordpress is widely enough used that you can do almost anything with it! You can manage others sites in terms of cheap hosting and managing their backend; manage Wordpress security; Wordpress specific consulting; create plugins that generate revenue; give talks on Wordpress; the list goes on and on!
If you become a Wordpress expert the sky is the limit!
There are a lot of options. Building Wordpress sites is where building websites in DreamWeaver was around 2004. Everybody is building Wordpress sites but most are not setting their clients up for success by properly securing the sites, offering SEO that actually produces results, and ongoing support to help them grow.
There are many opportunities such as hosting WordPress sites, consulting on WordPress, offering security services, starting your own theme and/or plugin marketplace, etc.
You can even niche it down further. For example, managing WordPress sites for doctors or lawyers.
Pick a niche, then pick an aspect of WordPress you'd like to specialize in (hosting, security, plugins, consulting) and go from there.