As Numismatic Overhaul offers a great addition to customizable village trades, it would be interesting to expand on those possibilities.

1. Add "tag" type to "sell" and "buy" categories. If a barter items is declared as a tag, grab all items from that tag, pick at random and parse as barter item. If possible, the random item pick from tag list should be per villager entity instance and not by profession-type.
   Only tag-based trading without picking one item at random from the tag-list would probably not work for "sell"-category. It would still offer an interesting addition at least for the "buy"-category.

This would render villager trading more dynamic and give modpack creators and players alike more options to easily add barter items in bulk to the game, hence further aiding on the idea of villager interactions and village gameplay. With this players could be motivated to have multiple instances of villagers if the same profession to gather additional items.

3. Add a default/general Villager Trade Data object to inject in all professions. Same data structure, just applicable to all professions at once.

1. You can create sell offers using tags (numismatic-overhaul:sell_tag). This is used among the Cartographer, the Mason, and the Shepherd. This is actually not documented over at the Wiki.
2. Tag-based buying doesn't make sense as buying is not planned to be implemented at this time.
3. Global Villager trades... not sure about this, as a big philosophy of the latest Minecraft updates has been to diversify villagers. It seems like a neat idea though, but could lead to some issues if you need the trade for 9/10 villagers (how should you exclude them? Opt-out per trade? Blacklist for the profession?)

Ah, great, thanks!

2. Tag-based buying doesn't make sense as buying is not planned to be implemented at this time.

I don't quite understand what is not implemented at this time? If sell_tag is implemented for sell_stack, would buy_tag not make sense, too? For Farmers - for example - to buy one in #vegetable or Mason to buy one in #sand? It just seems quite obvious to me, especially if sell_tag is already implemented. :)

3. Global Villager trades... not sure about this, as a big philosophy of the latest Minecraft updates has been to diversify villagers. It seems like a neat idea though, but could lead to some issues if you need the trade for 9/10 villagers (how should you exclude them? Opt-out per trade? Blacklist for the profession?)

Exclude or include profession could make this quite flexible - even thinking of maybe allowing for more data to be recognized. Don't see the major benefit though...

In case you don't think this is a good addition to Numismatic Overhaul and don't want to implement this feature: can we get in touch about me using a modified version for a modpack?

3. Global Villager trades... not sure about this, as a big philosophy of the latest Minecraft updates has been to diversify villagers. It seems like a neat idea though, but could lead to some issues if you need the trade for 9/10 villagers (how should you exclude them? Opt-out per trade? Blacklist for the profession?)

Thought about this a bit more. My proposed solution would be adding one more parameter to the profession.json to opt-in on parent. Parent can be any other profession or newly created jsons with same structure:

{
"profession": "profession",
"parent": parentname // defaults to "none"
"trades": ...
}

If "parent" parameter is set, check if "parent" is valid, then merge all "trades" from "parent".