While they have hinted at adding more skill lines, I'm skeptical it'd be any of those (considering everyone can sneak, and destro/resto staves already have lines).
Well, thieves guild and The Dark Brotherhood will be in the game in the future and I suppose those guilds will bring some stealthy skill lines among them.
There are already Destruction and Restoration lines.
Sneak will probably be taken care of by the Dark Brotherhood and Thieves Guild skill lines that are supposedly incoming. Its also partially handled by Nightblade.
I suspect we'll see many more as time goes on, hopefully including Necromancy.
@NordJitsu - Guild Master (Main Character = Hlaalu Idas)