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.
It's not like there's an actual "official LN launch" date or anything like that.
Rather LN will be "launched" when people feel confident enough....Okay I just figured out how to launch LN in a way everyone will understand.
THE DAY A PIZZA WAS BOUGHT WITH LN!!!!!
(Echoing the famous bitcoin pizza purchase of course)
Or even better....
THE DAY 10,000 PIZZAS WERE BOUGHT WITH LN