League of Legends (LoL) Question: Twitch jungler still viable after rework ? [SEASON 3]

For your definition of viable yes. Technically you can win a ranked game with any champion.
As for usefulness though twitch is much better as an ADC. His jungle leaves him extremely weak which leads to problems such as being prone to counter-jungling, inable to react for counterganks, etc.

It works sure, but it's so niche that no one would ever want to do it. Think about other niche junglers as well. Heimer can jungle. Annie can jungle. They don't jungle however because they're much weaker than other picks.

Remember having the ability to clear the jungle / gank doesn't make a good jungler.

I watched Saintvicious play jungle Twitch the other day, and it works fairly well. I suggest you max e before q to improve his clear and dmg output. Twitch jungle can snowball the heck out of a game, but only in the right team comps. Despite his sick ganks, he is much more effective as an adc. The jungle doesnt give the massive amount of gold an effective adc build requires, plus the jungle monsters dont exactly like rats. He takes a lot of dmg in the jungle.