I would love to see some kind of "Material Parameter Set" feature, selectable within material instances to avoid entering many values over and over again. Let me provide a simplified example, one image tells more than 1000 words

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The left shows the very basic material with the default values. This just blends 2 material function outputs (MF_base and MF_extra) based on a mask, while these material functions provide different parameters (here reduced to color, metalness and roughness, but could be any values, that are possible to be used with material instances)

In the middle, we have 2 material instances based on that material, with different "sets of values" for 'Base' and 'Extra'.
On the right, we want to create a new material instance, using values for 'extra' same as with instance 1 and values for 'base' same as with instance2. In order to achieve this, we need to enter all 6 values manually. Not a huge problem with these 3 values only, but in reality, we might have many more values to be reentered many more times if creating more instances.

So it would be nice to be able to define "Material Parameter Sets", somewhat similar to material parameter collections, but not restricted to scalar and vector values and useable from within material instances. Example: Create 'MPS_Extra1', which defines a set of values as used for Extra Group in Instance1. MPS_Base2 - same with base values for Instance2. And more...

Now, for Instance 3: There should be a dropdown option to select a "Material Parameter Set" - so as an alternative to entering color, metalness and rougness values separately, just select the MPS you like to use, e.g. MPS_BaseX and MPS_ExtraX, for which all value combinations are already prepared.