First and foremost, the whole thing was scrapped by valve, so the topic's not particularly relevant anymore. That said, when it WAS up, the modders actually got 25% of the price of the mod. Still not a fair split, imo, out of the money they received, but definitely better than 10%.
Still, honestly, my stance on it is that there should just be an optional donate-button. A mod takes a lot of work, sometimes, sure, but you're still starting off of a base game. Yes, they absolutely deserve credit for what they've made, but as they didn't make their own game, nor do they ensure that the mod will actually WORK for everyone, so no, I don't believe modders deserve to actually be paid for it.