Robert, it might be feasible if you can get enough sellers to join in, but I understand a very small percentage of them actually read the forums, so good luck with that. 

Also, I think you might need to change the wording to read that it is a protest against Ebay's policy rather than stating it is against the law.  We may think it is, but to be honest I expect Ebay's legal team have done their homework on this one just as they did on the fvf on postage thing.  If challenged it is more than likely that the result would be that it doesn't actually breach the law (T&C and all that).  In which case, you might be in trouble for libel.