If your time series is nonstationary in the sense that it has a unit root, it will not tend to any fixed value over time. Hence, trying to find such a value would not make sense. You either have to change the assumption from nonstationary to stationary or give up the target. You could also model the process as nonstationary within some interval but mean-reverting once it breaks out of the interval. That would imply very large inflation or deflation would not persist, perhaps because of central bank interventions, while moderate inflation would be approximately free of interventions and would not tend to a concrete value as long as it remains moderate. In such a case, defining a target could make sense.

If your time series is nonstationary in the sense that it has a unit root, it will not tend to any fixed value over time. Hence, trying to find such a value would not make sense. You either have to change the assumption from nonstationary to stationary or give up the target. 

You could also model the process as nonstationary within some interval but mean-reverting once it breaks out of the interval. That would imply very large inflation or deflation would not persist, perhaps because of central bank interventions, while moderate inflation would be approximately free of interventions and would not tend to a concrete value as long as it remains moderate. In such a case, defining a target could make sense.