I think source 2 will release with Half-Life 3!
http://www.quickmeme.com/img/7b/7b26db37fe4d3e5ad215737b752ce18ea4362798678f87d8a85126658d6c484d.jpg
Its already had its alpha release, but yes I'd have to agree I expect the first non alpha/beta build to ship with hl3.
that would be an amazing thing if it came out with source2........... i would be so happy