Do not worry about the Rebirth System of TOS
Haha, if you knew about the rebirth system from Ragnarok Online, you wouldn't suggest that. Jokes aside though, rebirth may come sooner or later, maybe even with story involved, unless they want to do maps with monster levels over 1000 later on. Best possible setting is that the world actually gets destroyed and recreated later on, making you depart from one game world to the other without the possibility to return...
However, I strongly encourage everyone not to panic since we will probably still have 3 or 4 Ranks more to come until OBT ends, with the possibilities to save their builds with the Rank 9 classes (who will possibly be the strongest ones to come out unless there are going to be Rank 10 classes).
Until then, I don't think IMC should make class/circle resets, because it wouldn't help anyway: people are bound to make mistakes at every possible circle, because they can't see or decide where the game/destiny is leading them. Yesterdays meta can become todays sh!tbuilds because monsters constantly change and are getting stronger&tougher.
This will cause people to abandon many ideas/classes in the process and making them cry hard for resets every single time something changes. This will harm essentially the class variety in the game because people are tempted by taking the easy way and then find the game annoying if they have to make an alt for more challenge/utility/etc. because it's very very boring to do so.
And now imagine what's happening if IMC actually decides to apply a major rework of a certain class with new attributes/changed skill scaling/utility [because of the communities feedback and suggestions]; how often are you actually willing to reset something?
If you did reset from that class to another that's now worse than your previous class, wouldn't you become extremely angry?
I've seen that many times in many different MMORPGs already, and I have to say : their fault for not rerolling another character. Until the game is out of Beta this is bound to happen several times, so you can just keep your character for later on and then play it again once they decide to boost it.
Or you could do it like many other players who are not so eager to Betatest games: stop playing now and start playing later on, saving you time and money to do something productive (like learning how to program and get hired by IMC to change the game e.g. xD ).