is there going to be a second class that the ninja can turn into?
No.
Actually, there has been an announcement that sometime after episode 14.2 (kRO is at 14.1 at the moment) there will be 5 new classes that will come after Ninja, Gunslinger, Star Gladiator, Soul Linker, and Super Novice so that those classes can advance to level 150 and somewhat be on par with third classes.
I'd expect it sometime near the end of the year or sometime early next year.
Read here:
http://www.eathena.ws/board/index.php?showtopic=241941
and look here:
http://www.onlinegamer.jp/news/15000/image/36/
There will be advanced classes for Ninja and Gunslinger soon, however, to fully enjoy them, I'd prefer playing official servers like kRO. iRO will get Renewal soon, too.