In recent years, Chile has really been pushing to be THE jumping off point for Antarctic cruises. Still it seems that cruises were pretty evenly going from Punta Arenas in Chile and Ushuaia in Argentina with Ushuaia still being the main port for Antarctic bound cruises.
Chile has been luring cruise ships with various incentives including reducing port fees if they stop in more than one Chilean port. According to this article, Ushuaia is really beginning to feel the squeeze, as it tries to increase port fees and Chile becomes more appealing to cruise operators with the incentives and better infrastructure.
While it seems bad for Ushuaia, I think they will still are a key port for Antarctic cruises, but will they be able to continue to compete with Chile? I would hope so, as I fondly remember it as a fun port to walk around and shop in before departing from the End of the World and Beginning of Everything (i.e. the motto of the city).