It's seems Sony is not entirelly fine with allowing more games to have crossplay. People need to keep pushing for this.

Finn Brice, the CEO of Chucklefish, which developed and published the recent Advance Wars-inspired hit Wargroove, took issue with Layden’s characterization in a thread about the interview on the gaming forum ResetEra.
“We made many requests for crossplay (both through our account manager and directly with higher ups) all the way up until release month,” Brice wrote. “We were told in no uncertain terms that it was not going to happen.”

https://kotaku.com/sony-says-its-open-for-business-on-ps4-cross-play-but-1832570505

Why crossplay is important?

Respawn wants to add crossplay to Apex

Lead Producer at Respawn, Drew McCoy, told Eurogamer that the developer "plans to allow players to play with their friends on other platforms" sometime in the future.

https://www.ign.com/articles/2019/02/07/titanfall-devs-battle-royale-apex-legends-officially-revealed

EA looks for crossplay in future titles.

"We think cross-play and cross-progress is going to be a very important part of our future, and you should anticipate that we'll be doing more in that space," Wilson said. "What our information would suggest to us is that there isn't a tremendous amount of play across devices, but that overall liquidity in any gaming community is a good and positive thing, even if it's only a few people or a small portion of the community that utilizes that.

https://www.ign.com/articles/2019/02/07/titanfall-devs-battle-royale-apex-legends-officially-revealed

HiRez and Gaijin are pushing sony to accept crossplay.

@el-shmiablo I believe are tools for developers to make their multiplayer games based on XBL, so it could have crossplay. I guess it's aimed towards indie developers to ease their development workload. Probably that's why MS hired Damon Baker. Most certainly Nintnedo and big publishers won't use this as they can afford their own online infraestructure.

At GDC 2019, Microsoft is set to debut a new cross-platform development platform with the goal of bringing Xbox Live support to games on Android, iOS, Nintendo Switch, in addition to PC and Xbox consoles.

https://www.windowscentral.com/microsoft-wants-bring-xbox-live-cross-platform-gaming-android-ios-nintendo-switch-and-more

Power Rangers Battle for the Grid and Wargroove will have crossplay

https://www.polygon.com/2019/1/18/18188207/power-rangers-battle-for-the-grid-switch-ps4-xbox-one-pc

Epic will make avaliable for unreal engine developers the tools that allowed crossplay in fortnite.
https://www.businessinsider.com/epic-games-cross-play-xbox-playstation-nintendo-pc-2018-12

Epic Games is releasing a totally free set of tools that are intended to break down the barriers between players on different game platforms.

There's no way back.

Paladins and SMITE will have crossplay and crossprogression between Xbox, PC and Switch.
https://www.hirezstudios.com/Crossplay/

Apparently, WarThunder already has Xbox, PS4 and PC crossplay.
https://www.gamerevolution.com/news/449291-war-thunder-xbox-one-ps4-cross-play