Thank you for asking for an example because I had to think more about it, trying to replicate more complex diagrams I have.
So, I have attached and .mdj file where there are two displays: left) Sort by Added, right) Sort by Name. The problem is obvious in this case, with very few components.
However, now I just focused on the fact that I only use "Sort by Name" because in the top-tiers models I use numbers in frond of the names like (000 [name], 010 [name], 020 [name], 025 [name], 030 [name]) in order to enforce a specific order when sorting by name. If I use "Sort by Added" everything breaks down, and I can't utilize the custom hierarchy that I have created and I need for quick hierarchical diagrams searching, in the models explorer.
But what I do - numbering in frond of the names of the models (not the components though because these are always visible) - is actually a workaround missing on a functionality: the capability to drag and drop my models in "Custom Sort" order.
So, my proposal about "Sorting by Type" probably would be an interesting feature that could group the Diagrams together, and additionally placing all the diagrams on the top, would be another add-on which would make it easy to have the diagrams available when we open our models, on the top side (thus this is actually 2 features!). However, I think a more advanced feature would be really handy here: The "Custom Sort" where I can drag a drop any model/component I want to any specific position before or after another model/component (this would be like the layers positioning of for instance S/W like inkscape/photoshop/etc.). However this feature which would be ideal (as we already can move models inside and outside other models like they are "layers", it seems easy to think it and use it), seems to me that it may need more work than the two feature I proposed at once just to solve the "detected" issue for my needs.
Thus, I shared my problems, ideas and workarounds.. I guess you will find the best way to solve such issues!