I don't have a problem with a reconsideration of the change after it has really had a chance to sink in. New Zealand's second referendum struck me as perfectly appropriate.
The notion, though, that we should experiment in 2019 with a system and then have a referendum strikes me as inappropriate. We will see the results of the election—they could surprise us—but I doubt that the parties would have settled into any kind of equilibrium, so to speak, response to the rules of the game, nor will we actually know the identity of the full set of parties that is likely to emerge.
A notion of a subsequent consultation strikes me as perfectly appropriate—just not in the immediate aftermath. The notion that somehow we could have a trial run in 2019, and then we'll do a different one in 2023 or something like that, just strikes me as nuts.