Take a deep breath and step back. I don't mean to be prejudiced but remember this is a young teacher who has only teached general ed. It's wonderful that she is trying so hard but it does not appear that she has seen very much. In my experience over the years with my own three children, this teacher's perspective may be colored by her lack of teaching experience and lack of a long-standing relationship with the adminstration.
I think it is perfectly fine to take the long view. To borrow a term from economics, consider taking the present value approach - today is worth more but the future is worth something too. There can be a huge difference between general ed classrom and gifted ed classroom. However, you know your own DS and you know the acceptable parameters for him/you. Do you think that he will likely be where you/he would want to be abilities-wise in the 2nd grade GT classroom next August?
I am somewhat troubled by her message that "he shouldn't be here" because based on my experience, it actually was easier for my three children's teachers to differentiate in K than in the higher grades. Assuming your DS is at the extreme end of the right tail abilities-wise, I don't think that sending him to first grade would improve his situation much unless the first grade teacher is far more experienced and able to differentiate far beyond the K teacher who is working hard and going above and beyond.
These are just random thoughts and not meant to persuade you one way or the other. It may be that your DS should be skipped and the 2nd grade GT classroom will be easy for him come August, but the timing of the skip would still need to be weighed.
