Your other tradable items are often traded no matter which platform you acquired them on Buy Rocket League Credits https://www.lolga.com/rocket-league , but you'll only initiate trades with players logged into an equivalent platform as you.
As a further anti-fraud measure, we'll also require both players involved in any trade to possess purchased a minimum of 500 Credits (players who played Rocket League before the launch of liberal to play are exempt from this requirement).
We're excited to bring cross-platform progression to Rocket League, and this is often only one of the new features coming to the sport when the update goes live later this summer. We still have tons of information to share as we approach launch https://www.lolga.com/ . So, stay tuned for more info at RocketLeague.com and follow us on Twitter for the newest news and announcements.