Just a few days ago Blizzard posted the thread I linked above. That said, I’m still unsure what Mod Support D2R will have. Taking a snip-it out of that post this is what they mention about Mod Support:
Blizzard still seems to be quite vague with what can/cannot be done. It seems like Multiplayer Mod Support is not allowed, but what about Single Player Mods such as PlugY? Will that be blocked as well?