My hunch is that this will never happen as long as cruise bennies are offered on a lifetime as opposed to a rolling basis. It serves the airline well to try and woo you away from a competitor, because if you have elite status then they know that you've spent a lot of time and money on air travel in the past year. And if you don't live up to your end of the bargain, your elite status wears off after just a year. There is no benefit to a cruise company matching your status earned through what could have been years of sporadic activity. You would now be "elite" forever on both cruise lines.