Pokémon Rumble Rush hasn't even been available in the US for a year yet (since it was originally released in the West in May 2019), and The Pokémon Company has already announced that it will close the game on July 22nd, 2020. Pokémon Rumble Rush clearly had issues during development, which is why it was originally known as Pokéland back in 2017, promptly falling off the map until 2019 when it reappeared under the new name, but was still under development. Once Pokémon Rumble Rush was officially launched across the globe in May 2019, it was clear the title was released as a cash grab to soak up money before the developer completely abandoned it, which we now know will take place this July.
Thanks to a report on Serebii, we have learned that Pokémon Rumble Rush will cease service on July 22nd, 2020, at 01:59 UTC, and as of today Poké Diamonds (the title's premium currency) will no longer be available for purchase. Refunds for this currency will be available until July 22nd, the day of closure, so if you still have a few Diamonds lying around, it's probably best that you either use them now or start the refund process.
Apparently, game events will still run for the time being, and so the Greninja and the Wonders of Kalos events will run from May 6th to May 27th. As for Battle Royale, the Shaymin Cup will run from April 22nd to May 6th, and the Zygarde Cup will run from May 13th to May 27th. Oh, and on May 27th, more Pokémon will be added to the title. Of course, if you'd prefer to read the Serebii snippet in full, I've pasted it below for convenience.
Pokémon Rumble Rush
It has been confirmed that Pokémon Rumble Rush will cease service on July 22nd 2020 at 01:59 UTC meaning it'll no longer be able to be downloaded, update or played. Alongside this, as of today, you will now longer be able to purchase any Poké Diamonds and there will be a refund for unused Diamonds starting July 22nd. With this, they have put out the plans until then.
Events: Greninja and the Wonders of Kalos - May 6th to May 27th 2020
Battle Royale: Shaymin Cup - April 22nd to May 6th, Zygarde Cup - May 13th - May 27th
On May 27h an update adding even more Pokémon will go live. You'll be able to goto many seas and see many Pokémon. Battle Royale w9ll be powered up with special participation requirements
As you can see, Pokémon Rumble Rush isn't long for this world, and despite the fact that this was clear last year when the game was released, I suppose it's still a bummer for the fans of this title to learn all of their hard work has been pointless. While I recognize this is the sort of situation where platitudes like "the journey matters more than the destination" are relevant, it's still hard to shake the idea that The Pokémon Company planned to cut this game's life short the second it wasn't profitable.