If that is your genuine concern, I'd suggest focussing on timeless topics. Two easy rule of thumbs: (1) if it's been around for a while and still relevant, it's probably going to stay that way (eg compilers/parsers, operating systems). (2) if it's hard and math-y, it has a good chance at staying power, even if new.
In any case, do what adyus said: pick one thing, and ship, ship, ship.
Some inspirational reading: Peter Norvig's "Teach Yourself Programming in Ten Years" (http://norvig.com/21-days.html), Richard Hamming's "You and Your Research" (https://www.cs.virginia.edu/~robins/YouAndYourResearch.html). Or if you are of a more entrepreneurial bend, P.T. Barnum's "The Art of Money Getting" (https://www.gutenberg.org/files/8581/8581-h/8581-h.htm)
Happy to talk in private. My email is in my profile.
(Some snark thrown in for free: forget about OOP design patterns.)