there is no ETA. lightning developers have taken the position that there is "no rush" considering how much value is expected to be stored in payment channels. they are very concerned about ensuring that no funds are lost as a result of using the LN protocol.

having said that, it's pretty widely expected that LN will be usable by the general public sometime this year, likely in a matter of months. the next major step is to complete wallet implementations. we're already seeing lightning transactions on the network; now it's mainly just a matter of releasing the software.