Smaller Dev's depend on engines like Unity, There is no reason why when that and other engines get DX12 they can't port ongoing projects over.
Its not about having to start a project as a DX12 project from fresh in DX12 when its here, its simply a matter of porting what you are already working on. Edit: well, its not quite that simple.
The mechanics of it are very different from back when DX10 became DX11.
True, but how easy is it for small developer who has started their project with older version of Unity, that doesn't support DX12. To upgrade their engine to new version and continue working from that?
Though gotta admit also that most games from smaller developers don't seem to be that demanding from hardware, that they will work out well enough on DX11 aswell. But there's always those few that are demanding.