Its 25% for the mod's author, 40% for Bethesda and 35% for Valve. From that 35% Valve gets, 5% can be distributed to "service providers" the mod's author think they helped to create the mod (think NifScope for models, SKSE for scripts, NexusMods for the community, etc).
According to Bethesda, Valve is taking their 30% standard cut. After that, the publisher decides the split of the remaining 70% (in this case, Bethesda chose a 45/25 split).
They've rolled it back anyway. It's a shame really, because I thought there was some merit in the idea. I liked that mod devs could either go fixed price, pay what you want, or free. 25% feels a bit low, but that's not Valves fault and 25% of something is still better than 100% of nothing.