Alright, so, this has to be per-game settings, because these issues aren't something true for all games.
First of all, please make it so that mods can be downloaded from the Workshop using things like
http://steamworkshopdownloader.com/. Many newer games (and some older, now, for some reason) allow this, and for example, Torchlight 2 allows it, as does other games, so it
can be done.
Second, allow those that do not own the game on Steam to actually post on the Steam Workshop (provided they have a Steam account, obviously). Many games allow this, such as XCOM 2, and it's very frustrating not even being able to ask the modders to share their mods outside of the Steam Workshop, or report issues to them.
And if you can't figure this out yourself, please talk to a Valve Steam rep about it, because from a modder perspective, these things are very annoying.
Edit: May have to scratch that second one, it could be a Steam-wide change and I can't actually find any workshops of games I don't own myself anymore in which I can comment.
Well then lodge a formal protest or something and tell Valve that they're being idiots, trying to forcibly split modding communities apart.
