Gaijin CEO Anton Yudintsev said that most, if not all developers are ready to enable full cross-play with the flip of a switch once Sony gives the green light.
He also pointed out that this will be only the first step anyway, with cross-platform voice chat and account migration/progress also needed.
Source: N4G PC Gaijin: Most if Not All Devs Are Ready to Enable Full Cross-Play;Voice Chat Should Also Be Supported