In an announcement made by the Psyonix Team, the crates will be replaced by 'a system that shows the exact items you're buying in advance'. They reference the change made by Epic in relation to Fortnite's Save the World mode, which switched 'Loot Llamas' for a clearer system of acquiring items called 'X-Ray Llamas', showing the item inside before you purchase it.
Multiple games have faced backlash over the inclusion of 'loot boxes' to encourage in-game microtransactions. Star Wars Battlefront II was the catalyst for public scrutiny which has seen governments discuss the topic and calls for their removal, classification as gambling or forcing games that include them to be rated Mature have grown.
With Epic taking control of Rocket League, it is possible items move towards a Fortnite style means of acquisition, relying on luck and timing to get desirable items. This would ensure the game avoids any possible penalties or restrictions future anti-loot box legislation could bring.
It is unknown what will happen to Keys used to open Crates bought with actual cash and the knock-on effect for traders. The r/RocketLeagueExchange subreddit has a megathread set up where many have expressed their concerns for those who have invested heavily and for items that were previously valued highly in the RL market.
Questions have also been raised over whether purchased items will be untradeable like those bought from the Esports Shop, where specific items are displayed every 24 hours and are available to buy in that timeframe. The Crate change will have no impact on this shop, Rocket Pass Premium or DLC Cars that will continue to be offered in-game.
Nothing else has been said by Psyonix on the matter, with no further information or dates for the removal.