Information posted by the SteamDB website indicates that Dota 2 could soon be running on the Source 2 engine. The site lists several "changed depots" for the game that reference "Source 2 Dota 2 Content" for 32 and 64-bit Windows, as well as Mac and Linux, in multiple languages.
The impact of that is currently a matter of speculation, but as VentureBeat explains, Source 2 is essentially an updated engine and toolset used for game and content creation. Dota 2 is built on the Source engine, so a move to Source 2 could mean new features, more advanced graphical options, plus a wider and/or more flexible range of tools for mod makers. Valve announced in March that the Source 2 engine will be free for everyone, with the proviso that any games made with it must be sold through Steam.
We've reached out to Valve to see what the ramifications are, and will update if and when we receive a reply.