If you ask Zuckerberg, it's VR.
Musk, it's batteries, then space transit, the Mars.
Bezos, it's media power.
Google/Alphabet, it's sort form of self-driving map-navigating vehicle.
Microsoft, it's whatever the next startup they acquire is working on.
For smartphones, it's wafer-thin clear devices that are basically: ID card, credit card, smartphone in one. 2025?
For old people, it's personal robotic assistance.
For travel, it's "multi country visas" (like Schengen in EU or CTA in IE / UK, but for more and more regions that are not in a combined area), but also: "multi product travel agents", like you just go to the app, pick your next city, and you'll see a couple of price tiers of package, with each automatically taking care of: your hotel booking, your flights, your airport to hotel transport, plus any data sims, and other basics you need. And then it works the same for every city you want to go. Just works.