I have two MacBook Air 5,2 models -- one I clean installed Beta 3 and one I updated from B2U1 to Beta 3.
If I single-user boot both of them -- the keyboard (even an external one) is not working.
I reverted one of them back to 10.12.5 and single-user boot works as expected.
This is a pretty bad bug (considering the "dsconfigad" bug is not fixed yet!)