That is actually legally impossible. If you give someone such leeway as Hasbro is giving us in terms of fan art and other derivative works for a such a long time, we're coming up on 3 years in a month, then you are legally giving them a license to do such things.
Long story short, we've been doing it for so long without C&D's on everything that we are now allowed to do it whether Hasbro likes it or not under US law.
Edit: BIG WARNING! I am very confident in my interpretation of the law, and many others agree with my interpretation, but this is in no way legal advice, and I am not responsible if you using my post gets you in trouble somehow.