The MI (Multiple Intelligences) theory is important in understanding and dealing with the human being from an open, wide, and real holestic perspective. If instructors studied the theory and became  even experts in it, ready for change, will that be enough to start talking about having an MI classroom? 

Many parties involved  

School teachers, training centers instructors, and educational administrators, are just at the end of a long chain of other people in the decision making and policy making systems. As a teacher or instructor, when you try to apply a MI concepts or implementations in your own classroom, that should be already recognized from the top-level policy reviewers and administrators, because that definitly reflects itself in all the educational processes you practice, and all tasks you are to do. 

For example, if you considered the difference in intelligence attitudes, and wanted to give different  type of assignments to different groups of students in your class, accourding to a chart of different interests and capabilities, will that be acceptable in the system? 
If you wanted for instance to talk about brain nutrition and its role in the learning process, and the material you are teaching is something far away from life sciences, will that be considered as time-wasting extra-curricular, or skills teaching? it depends on how the system in your country, city, and more particularly: your school looks to it. 

Considering Brain Compatibility in assesment systems 

Assesment systems and evaluation methods' guidelines usually come from the top level educational authorities in almost all countries (Assessment Drives Instruction..in many cases ). No teacher or instructor is left alone to his own assesment criteria, granting the students their points and grades according to what he believes priorities and measures. In this context, I recommend the reader to act within his own frame of authority and control, 
with full devotion to develop the system with recommendations, ideas, and studies as possible. 
On the classroom level, the teacher can apply "a lot" of techniques, that fit into any instructional system, with great success and more higher results. This is the area I made this web site about, and it doesn't need any authority to approve or to direct any conceptual or practical application to make the learning process brain-friendly, or brain-based.