It's not going to be entire roles being pointless, it's going to be about certain heroes being better then others.
From what I've noticed, the best chars are either Good Duelers, Long Distance harassers (kog-maw for example) or tanky. With mobility being a great thing to have on anyone.
Shaco and Twitch are going to be powerful due to their stealth. With people constantly dying all the time in order to secure points and defend them, Oracles will be a huge waste of money to constantly use.
On the other hand, heroes who focus on only AoE are a lot less strong.