Putting the Professional in Teaching Part II

In my previous post, I suggested a potential model for teacher compensation that took ideas from the professional sports landscape. Before I began to put words to the digital page, I knew there would be issues with such a model because it would be a radical shift from the current model and today I want to address some of those issues.  I don't necessarily have suggestions, but want to identify the holes in my thoughts and maybe there is someone else who can provide further ideas.

Funding
Under the current system of funding schools, there is no way that this system would be tenable. What a great thing though if we could forecast the actual amount of money that schools would be allocated for a period of five years. The long range planning that a school could do would allow for a true vision to take shape and allow a pool of money to be saved for those years in the future when a shortfall is envisioned.
As with "market based pay plans" funding is going to be an issue. When I hear of this market based pay in our district, I question where the money is going to come from when teachers hit the benchmarks that trigger a pay increase when there is no money in the district to begin with! 
Does the proposed system potentially set up a rationed education in subject areas that aren't considered as important as another subject?

Subjective Negotiations
How we evaluate teachers would have to be reconsidered, I am not a proponent of standardized testing that suggests the effectiveness of a teacher merely upon a test(s) that students may or may not have an incentive/buy-in to perform well on. Another part of this would rely upon Admin to be very aware of their staff and perhaps bias would infiltrate this examination about the importance of one teacher versus another.
Another aspect of this that is potentially flawed is that by offering contracts to teachers is it based upon their abilities as a teacher or is it for additional credentials that they bring with them (say coaching). However, one's involvement in activities that extend beyond the school day should/could be valued under this system in that they are helping to mentor students beyond the classroom. The glaring issue with this though would be a potential loophole that leads to schools rewarding say their football coach with an excessive teaching contract that isn't necessarily "earned" for their performance between the first and last bell of the day!

Union
This might be the big obstacle, having been a member as a teacher and as a former professional lacrosse player change is always difficult. If pro sports can have differentiated salaries based upon an agreed upon pay scale system, why can't teachers? As a Social Studies teacher, I realize that I am very unlikely to ever top out with a "maximum dollar" contract in the proposed system, but feel confident in the abilities that I demonstrate that I would warrant a quality salary.

Simply put these are a few issues that I have with my own proposed system. Could it work if we really worked on ironing out the issues? Why not, however the first step is getting a funding system that doesn't limit the education that we provide our students. To remain at the top, we cannot simply rely upon a small percentage of our students to achieve, the better educated a society the more productive it can be.