One of the reasons that mods have always been free is that it is not appropriate or ethical to make money off of someone else's IP. I expect that crossover mods that do not involve only Bethesda (and perhaps Valve) properties will not appear. Bethesda is being more generous than they need to be by accepting only half of the profits made on their IP. That said, it may be exactly as generous as they need to be to be able to make anything off of it at all, since modders have to be encouraged to change their hobby model into a side business model.
But it does look pretty messy at this point. Officially selling user-made mods is a new thing, it will have kinks and issues and may not work out. We'll see what they do.
As an experiment, it may prove that all the underhanded money-grabbing tactics used by big business that we all complain about will be freely used by their consumers when given half a chance. The long term goal of this enterprise may be to split the consumer base down the middle and rob us of our right to bitch, which must get annoying for developers and publishers after a while. In which case, once again someone must utter the words "Well fucking played, Valve."
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