In a recent update to the beta version of Artifact 2.0, there was some mention of ray tracing shaders and RTX rendering. Most likely, support for the above technologies will be added to Source 2.
But the main snag is why such updates to Source 2. It is unlikely that RTX will appear in Dota 2, Dota Underlords or Artifact. Perhaps Valve is doing this for future projects. Although it is possible that such technologies can be added to Half-Life: Alyx.