It could obviously be made into anything related to programming (tutorials, mentoring or freelance marketplace, Q&A format forum, etc.)
If you're interested, you can check out the auction here (ends in 2 days): https://flippa.com/10635953-programming-io
I don't know anyone who looks for things related to programming by going directly on programming.com.
If i was looking for insurance, I wouldn't just go on insurance.com either.
What's the benefit of owning this type of domain?
People are unlikely to visit "programming.io" and then search something specific, but if it becomes popular for a particular type of content or tone or niche purely through organic search, people will include an easy-to-remember domain in the search query. Remembering "programming.io <query>" is easier than "johndoereactjsdev.blogger.com <query>".
It's not uncommon either. Just run a random tech search and notice how many hits are under generic "tec*" domains that publish how-to articles on multiple topics.