I've made a few mods in my day, usually just for myself or a few forum users, but I sincerely think that this is a terrible idea.

The whole point of being a PC gamer is that it's a relatively open environment where new ideas can develop free of platform owners and developers oversight. Selling mods constitutes a contract between whoever made it and the person who buys it. It's not just a bit of fun anymore, suddenly mod creators are obliged to continuously support their work as developers update or change their game because someone paid for it.

Now what happens when a mod creator goes dark and their project doesn't work with the current build of their game? It's bad enough that this is happening with full release titles, let alone individual mods. Will these people be entitled to a refund?

This needs to be an optional payment - I appreciate that you can choose how much you want to pay, but it should be used as a tip jar rather than a purchase. This should also apply to full games which would otherwise be free; for example if Dwarf Fortress were to release on Steam, I'd happily throw them a few quid I made off of selling trading cards or whatever. But what we can't lose sight of is that this kind of content has to be free if it's ever going to become popular in the first place.

So, does that mean that mod creators don't deserve to make money off of their mods? It has to be looked at on a case by case basis; for example the DayZ mod for Arma 2 essentially created a whole new game out of one person's work and existing assets from the base game. The amount of content it offered justified it becoming a standalone game. These are the kinds of mods which deserve to make revenue, not individual assets or game design tweaks.