P: Customizable groups for quick collection

Thanks, this will definitely help with organization.
It still lacks visibility for larger quantities, but nevertheless this will be useful.

Maybe this will help: if you look in the metadata for images, the colour setting is simply a label setting, and it can be set to other text.  This text is then usable in a smart collection set using the Label Text (rather that Label Color). Another method could be to add a coded keyword (eg Amotif, Bmotif etc) added to each required grouping - keywords can be more flexibly searched in smart collections. You can quickly apply the labels or keywords using the painter tool.

First of all thanks for your response. 
I'm familiar with (target) collections but that's not what I was aiming for with my idea. It doesn't quite do the trick in this regard and it is a bit too fiddly.

I try to clarify my point with an example:
Let's say I have a project for a client. The client needs a certain amount of images per motif a, b, c, d... s, t.
If I add a collection for every motif this quickly gets confusing as I do not have a total oversight and ideally I want to keep them in one collection in the first place.
With the idea of customizable groups there would be a tool to better distinguish smaller categories.

I often photograph trainings with several participants, so this situation is quite familiar to me.
Another example would be larger photobook projects with many different sections which could benefit from this.

I apologize if this thing is bit a too special interest.

You're clearly into the domain of using Collection Sets and Target Collections for a little more power that the Quick Collection provides. Target Collections are just collections that take on the roll of the Quick Collection, which you can of course add colour labels to. 

Moved to Ideas so others can upvote.