When Valve announced Half-Life: Alyx last year, it said that a level editor would be available to the public, a commitment that remains on the Alyx website. "A set of Source 2 tools for building new levels will be available for the game, enabling any player to build and contribute new environments for the community to enjoy," it says. "Hammer, Valve’s level authoring tool, has been updated with all of the game's virtual reality gameplay tools and components."
The Half-Life: Alyx listing on Steam also says that a level editor is included with the game, although that's not currently the case. But in case you had doubts (or forgot about it completely), Valve developer Jake Rodkin confirmed on Resetera that it's still happening—and, in fact, it's now the development team's priority.
"It’s the team's focus now that the game’s out. There will be more info soon but we’re working on it," Rodkin wrote. "Sorry I don’t have a date beyond that but I’m sure there will be more communication soon. Most of last week was spent on post-launch patching and tech support."
Modders have already been hard at work bringing Alyx to non-VR setups, and while early efforts have been fruitful, they've also been supremely janky and not really playable in any kind of proper sense. Access to the level editing toolset could be a big help in those efforts, depending on how it's implemented (Valve said in an AMA earlier this year that it's not planning on releasing the full SDK).
That said, there's of course the potential for new, user-created VR worlds. Maybe a headcrab sports arena, for starters?
