Die Aussagen stammen vom Psyonix Vice President Jeremy Dunham...

"In terms of pure greenlighting for when this project started, three months ago. If you wanna talk about when we first started investigating, messing with dev kits, late last year was about when we first started looking at it."

Nintendo first contacted Psyonix about a potential Switch port before the platform was officially announced
Mario Kart 8 Deluxe's success was a huge motivator for the Psyonix team to get the game right on Switch
once again, the game runs at 720p at 60FPS (docked and undocked) Rocket League isn't the most graphically challenging game, but it's very dependent on the physics
this is why the team didn't go for a better resolution
8-player local multiplayer
two-player split screen on a single Switch with each player using a single Joy-Con
year two DLC releases include a new anniversary stage, customizable explosions, and some other aesthetic goodies

QUELLE: http://gonintendo.com/stories/282995-nintendo-contacted-psyonix-about-rocket-league-before-switch-s-of

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