Pokemon Rumble Rush is shutting down.
The official Pokemon website confirmed the news, putting the app's end-of-service date on July 21, 2020 at 6:59pm PDT. Rumble Rush has preemptively shut down purchases of Poke Diamonds, the microtransaction currency, though you'll still be able to use them up to the end of the game's life.
From the American version of the site it says just says to make sure you spend them all before the game shuts down.
So Pokemon Rumble Rush is on its way out and there is a still BIG update comming for the game planned to be released by the end of may the update will add "more Pokemon than have ever appeared before to the game," including some rare and powerful specimens. The Battle Royale mode will also get some new effects from special summon gears for Pokemon.
You don't usually see big updates like that roll out just a few months before a game is scheduled to go offline, which could be the developers were surprised with the discontinuation of service.
It's really sad to see any game go so soon, though I doubt Rush will be the last Pokemon Rumble. The subseries first started as a downloadable Wii game back in 2009, and it's been sending waves of clockwork Pokemon toys into battle with one another ever since.