depends. They can either give him the Trundle/Udry/Leona treatment and just not even give him any new skins, or they can give him the Ziggs treatment and release two new skins in the span of a few months.
Well, even if he ends up becoming a popular champion to make skins for, it's far too early for him to get another one anytime soon, based on how it's been for other champions. If they're anything to go by, you shouldn't expect anything for about five months after the champion's release, so Deep Terror's the only thing Thresh is gonna have for a while.
The time is out of joint. O cursed spite, that ever I was born to set it right! http://i.imgur.com/pyvQmyz.gif
I can't see Thresh getting one soon, I wouldn't mind a new Thresh skin though, I hate the colour scheme on his release skin. I want Diana to get a new skin first though and I think she'll be getting one soon.