Warning: Humongous Wall of Text.
First things first: I myself am not a modder (yet).

We have many mods, and many of them implement new materials, and many of them in many different materials.
A prime example is glass / sand. I know at least three mods that implement glass, and all three use different materials.
In real life, glass is of course made by melting sand. However, sand doesn't exist in ME (yet™?).
So one mod produces its glass by melting dirt and metal parts in a furnace (creating already placeable glass tiles), the second by melting clay and flax in a kiln (creating a glass pane material for further crafting, also used in other mods), and the third by melting rough sand (produced by grinding small stones) and flax in a kiln, also creating panes for further crafting.
Of course, the respective modders could have sat together and decide on a common sand and/or glass material, but that would create interdependency, which I think should be avoided since it makes things very confusing in general, and can cause problems if one of the group decides to give up on modding or ME in general, especially for the mod users.
If there were a common sand or glass material already in the game -- not actually implemented as items, just as entries in a material list --, this could be avoided. I believe something similar already exists for sticks/branches, logs (for all trees), timber (square, round, diagonal) etc. - but only for things that already exist in the game.

Let's say modder Sandy decides to make the existing sand voxel to actually yield a sand item, which can be used in crafting. This Sandy-sand uses the common sand tag, and becomes rather popular.
Modder Glassy uses Sandy's sand item for his glass mod. The resulting glass item uses the common glass tag.
Modder Paney also makes a glass mod, which is produced at her very own glass kiln, also using the common glass tag. Her kiln is pretty late-game.
Modder Bill is a big fan of windows, and creates a window block, which requires glass. Because of the common glass tag, users can decide whether to use Glassy's or Paney's mod.
Modder Sandlord decides that Sandy's mod yields too much sand, and decides that the sand voxel should yield half as much of his own superior Sandlord-sand, which can only be mined with the Red Herring, but at least also using the common sand tag.
One day, Sandy becomes a mom and doesn't have enough time for anything anymore, especially modding.
Sandlord, Glassy, Paney and Bill still have plenty of time.

Boom. New big release. Everything is different (Maybe? If you guys intend to do so).
Sandy won't update her sand mod.
Under current circumstances, Glassy and Paney (and in consequence, also Bill) would be kind of screwed, and they would have to rewrite his mods, to either use their own version of sand, or use Sandlord-sand (Sandlord is kind of a douche, so meh (I know, I know, everyone is super nice in this community, let's just pretend someone like Sandlord shows up one day)).
With a common material list, this is not a problem. Glassy and Paney simply have to adjust to the changes in the game, without having to deal with Sandlord's shenanigans. It's only up to the mod user whose sand mod to subscribe to.

And all this takes is a simple list of material tags already in the game.
For starters, I suggest the following, common items:

• Sand
• Sandstone
• Gravel
• Glass
• Limestone
• Quicklime
• Concrete / Opus caementitium
• Brick
• Bone
• Bone meal
• Wheat straw (separated from the seed)
• Flax stalks (separated from the seed)
• Brass ingot
• Zinc ingot
• Zinc dust
• Zinc ore
• Sulfur
• Saltpeter / brimstone / potassium nitrate
• Gun powder
• (Plant) fibres

... just to name a few. If a modder were to come up with another great material that could be of use for other modders, they could tell you guys or simply comment on this here ticket.