DarkPenguin, thank you very much for the explanation! I was looking at the "stacks" post(s) quickly, but didn't quite understand what was going on, so i lost interest in the topic.
I'd say it's crucial to rename one of the two functionalities you were explaining. If i got that right, we have two basic functions:
1. Combination of single "files" (tracks/images/videos/etc.) into one "stack", mainly for viewing purposes (choosing the "best" of the files as the one visible on top of the stack, etc.)
2. Grouping of similar or identical files, mainly for organizational purposes. Tags would apply to all files in that group, etc.
I'd say that "stack" is a logical choice of wording for #1, as the metaphor is easy to grasp and understand (a stack of media files). But #2 is completely different in functionality, IMO. I'd prefer having this called a "group" or a "set".
I have to say that i'm quite excited about #2 especially. In my collection, i have multiple versions of the same audio track (song), for example - on a sampler, on an album, on a single. Right now, i'm using a special tag (which i've called "dupe") to identify a "master" file (where the "dupe" tag would be "1"), and the "slave" files (where the "dupe" tag would be "2"). This approach is only a workaround, of course - i have to keep the tags in sync manually, for example. This is very time-consuming and frustrating, especially for a large collection. The possibility to group several files together to one logical entity would be a major enhancement of MC's media management functionality, IMO.
P.S.: i hope you were only joking when you wrote you'd call one of the functions "Flacjacks". I'm a fan of the "KISS", and the "Form follows function" principles, so i'd prefer a term (or terms) that can be understood (more or less) intuitively. As you can see, even the relatively simple term "stack" is not easily understood.