The point is that the goal is far enough into the future that the person making it can't be held accountable for failing to meet it.

If Xi had said "the CCP is illegitimate unless it takes Taiwan by 2025", he would be at real risk of being replaced in 2026. Anyone who opposed him (or just wanted power) would have a perfect reason to replace him.

When Xi makes a goal with a "deadline" he won't live to see, he takes no risk of personally failing to meet the goal. If his successor misses the deadline, he can say things changed, Xi failed to consider factors X,Y,Z, etc.