Well...you might want to reconsider. Evaluations are now going to happen, and the result of a poor one is that you'll lose your job before the year is over. Now, I have nothing against employers evaluating their employees. And actually, I wish it would happen a lot, lot more at the uni level before decisions of contract renewal are made. At the uni, you teach alone, expectations are generally clear and how you run your class is entirely up to you. It seems much easier to evaluate someone's teaching skills in a situation like this.
However, the public schools are an entirely different matter. Like Brian says, no expectations combined with no plan to effectively use native speakers in the classroom makes for a tough situation for the foreigner. So how could they reasonably be evaluated when they don't actually know what they should be doing in the first place.
And, who exactly will be evaluating? Someone with a masters or Phd in education and years of experience teaching a second language? Someone who actually KNOWS English? Or will it be some head office guy who has never been in a classroom in his life and can't actually understand what is happening in the classroom.
And, will the evaluations be done randomly? If yes, perhaps head office will see how many native speakers are left totally alone in the classroom, and have become the head teacher, without the help of their co-teachers, despite only being "assistant teachers." Will there be some recourse for these lazy Korean teachers? Anyone can put on a little dog and pony show, but the real test is the random evaluation.
And, will people be "let go" at the 10/11 month mark? This could be an excuse to avoid paying airfare and bonus money in a quasi-legal-ish way.
Too many questions and no answers for a while. All I know is that I'd avoid public schools in Busan for a year or two until we see how this all shakes down.