As reported by Windows Central, or spotted, Microsoft is hosting a GDC 2019 session called 'Xbox Live: Growing & Engaging Your Gaming Community Across iOS, Android, Switch, Xbox, and PC'. Which all but spells out its plans in the title. It's part of a new Xbox Development Kit that will integrate cross-play on the Xbox Live platform across multiple devices.
But not PlayStation - naturally. As per the description:
Xbox Live is expanding from 400M gaming devices and a reach to over 68M active players to over 2B devices with the release of our new cross-platform XDK.
Get a first look at the SDK to enable game developers to connect players between iOS, Android, and Switch in addition to Xbox and any game in the Microsoft Store on Windows PCs.
Xbox Live on other platforms isn't all that new, as Minecraft requires an Xbox Live login across Android, iOS, and Nintendo Switch. What seems to be new here is the tools for developers to integrate cross-play, in addition to online services including profiles and achievements and multiplayer etc, in any title developed for these platforms. With Microsoft's cloud gaming service Project xCloud also on the horizon this is very much a power move.
It's hard to predict exactly what will come from this, but going for broke - we'd love to see something like Sea of Thieves make its way to the Switch.