@Bengali Thank you and yes plagiarism should definitely something someone can flag. I just don't know how the system works for providing info on your cards, which is necessary since someone who doesn't know that you have permission could flag you.
@sprocket314 I don't know enough about The Spoils to comment on those cards. But you seem to exclude other possible cards that could crop up. Those which are racially insensitive, depict sexual acts, etc. I'm not against nudity in the cards, but there's a clear difference between nudity and sexual acts being shown. So the problem cards can run the gamut. Now you may say that pornographic content isn't really a problem since there could be a filter system. But it's all about public perception.
Not to go off on a tangent, but as an example I'll use Snapchat. Snapchat started out with the stigma that it was only really useful for sending limited time nudes. It took Facebook seeing Snapchat as a serious threat for other people to really see Snapchat for the potential it had. Now I know this is this and that is that, but there's a very good chance this game can get stigmatized if sexual acts are allowed on cards. On the other hand, nudes in art is generally in the grey zone. Look to Roman art for example. But this game getting maligned so early can put an effective stop to what they're trying to do and I believe that goal is more important since it's what will keep the game going. Making custom art is only one part of this endeavor.
Again, I do enjoy the freedom they are going to allow, I am an advocate for it. But there are still lines that must not be crossed because there are still rational and irrational people out there that could cause a more than just a stir.
As for the actual sets themselves, I don't think any of the art will inherently need to be age restricted since I doubt there will be such cards in base sets. But that's me assuming. Again a system of flagging, reviewing and banning both offending artists and irresponsible flaggers should be enough. At least I believe so.
By the way, I'm not trying to discount your opinion or anything of the sort. If I come off as gruff, it is not my intention. I always welcome the discussion anyway, especially if it's for helping out things like this.