I haven't read that there is the possibility for 'variable' margin that could occur any time out of the blue, except for the weekend rule of course, which they are pretty clear about. Have I missed a paragraph?
You know something? If you think the "house" is always out to get you and you have little or no chance of winning, don't trade it. Stick with futures and equities. As to variable margins, have you traded with IB or another futures broker lately? Have your margins stayed the same? Has the CME STOPPED raising/lowering margins from day to day? I read some of the posts from people here and it seems like you are looking for a reason to fail before you even try.