Fans of Splatoon 2 have been receiving regular free updates since the game was released in 2017, with a huge amount of content also being added in the paid Octo Expansion DLC.
The free updates for Splatoon 2 were due to end in December 2018, but it seems that the Squid Research Labs aren't shutting yet, as Nintendo has announced that more content is coming to the game.
The Japanese Splatoon 2 Twitter account has announced that new content will be coming to Splatoon 2 in the future, though the nature & timing of the content is still uncertain at the moment. We do know that ten weapons from the original Splatoon will be added to the game at some point in the future.
The Twitter account also announced that demo for Splatoon 2 will be running for a week, starting on March 26th, which will allow you to transfer your content into the retail version of the game, should you choose to purchase it.
As of now, the Splatoon 2 demo has only been announced for Japan, but it will almost certainly be made available in other countries as well. It would also be easy for international players to create a Japanese account on their Nintendo Switch and download the demo when it becomes available, should you be so inclined.
The fact that Nintendo is making such a fuss about Splatoon 2 when it is over a year old is likely related to the high sales of the Nintendo Switch over the holiday season. The Nintendo Switch has seen an incredible attach rate for games like Mario Kart 8 Deluxe, Super Mario Odyssey, and The Legend of Zelda: Breath of the Wild.
As of right now, Splatoon 2 is the fourth best-selling game on the Nintendo Switch, with 7.47 million copies sold, but it's trailing behind Breath of the Wild's numbers, as that game has sold 10.26 million copies to date.
It's possible that Nintendo wants to attract the new Nintendo Switch owners to Splatoon 2, as the system saw a huge surge in interest following the release of Pokémon: Let's Go Pikachu & Let's Go Eevee and Super Smash Bros. Ultimate over the holiday season.
The fact that Splatoon 2 is receiving more free updates also suggests that Nintendo might not be planning on releasing Splatoon 3 for a while now, so they want to keep interest in the series fresh with new content and possibly some more paid DLC further down the road.