Immigration Reform - "Back of the Line"

Obama said something interesting with his speech about comprehensive immigration reform the other day.  He said that illegal immigrants would need to go to the "back of the line".

For unskilled immigrants, there typically *IS* no line.  There is basically no way to legally come to the US, unless they are family members of existing US citizens. See the chart below.

So, I wonder what he was talking about?  I think immigration reform is a necessary step, but I'm really interested in how this is actually going to be implemented.