AI is already well underway, so that's probably the most plausible soonest.
A fully reusable rocket in the form of Starship is also well underway and should be successfully orbiting for the first time soon. Just a matter of a year or two before it's doing workhorse cargo launches probably.
The new round of superconductor possibility might pan out, which would be another one. But that's more of a yes/no outcome that hasn't quite been settled yet, rather than something with a "completion bar."