You present a persuasive argument for the abandonment of the 5-paragraph essay and suggest a new format for presenting an argument... However, you did not provide much information on what is expected to go in between your introduction and conclusion? You suggested this format opens the essay to compare/contrast, cause/effect, analysis, etc... but how do you suggest students structure an essay with these approaches in practice? Any piece of writing needs some structure and main ideas that are then supported with various pieces of evidence (whether you are writing a historical thesis or a persuasive essay)... If you are abandoning a "main idea followed by supporting evidence" format, what do you propose should take its place? Or perhaps my understanding of the 5-paragraph essay you are speaking of is incorrect?
It’s as well to keep in mind what you should not be doing. Do not introduce lots of fresh evidence at this stage, though you can certainly introduce the odd extra fact that clinches your case. Nor should you go on to the ‘next’ issue. If your question is about Hitler coming to power, you should not end by giving a summary of what he did once in power. Such an irrelevant ending will fail to win marks. Remember the point about answering ‘nothing but the question’? On the other hand, it may be that some of the things Hitler did after coming to power shed valuable light on why he came to power in the first place. If you can argue this convincingly, all well and good; but don’t expect the examiner to puzzle out relevance. Examiners are not expected to think; you must make your material explicitly relevant.