I was away for a while when writing, and now both foosion and jkwarras has posted the kind of thoughts I hoped for, when suggesting a thread like this. To look to other tag formats and players is a good idea. Comments from people like foosion is also very valuable, so that we have opinons from every group of users.
Whether the name of the date/time tag is changed or not, isn't that important to me, as long as it's well thought through, and easy to tell new users what to do, to make things work. But, having the new one as the default tag in foo_playcount is crucial, I guess. If a user's current format outputs garbage, with a certain formatting, just tell him where to look for an explanation for how things should be done/used. Some masstagger scrips that would reformat common, current formats, could also be provided. But, the way formatting devs extract info from the "new tag", will of course affect how successful the latter is (at least one should avoid the use of $right() ).
I also agree with picmixer regarding the use of %album artist% for VA tagging. Nowadays I use the same approach as him, but earlier I used %various%=yes, because I didn't have any experience with custom tags when I started. I later changed to %album artist% as it's more efficient, and has widespread use. This is one of the reasons I suggested this discussion in the first place, because when you're new to custom tags, you might not have a good reason to choose one format over the other, and hence a guideline like this could be useful. If (new) devs want to make a formatting that as many as possible can use, then following a guideline for the prefered way of doing things, can be useful. No need for everyone to reinvent the wheel.
My goal with this discussion was not to make a string that supports every possible way to mark VA albums and such. Been there, done that, and now I prefere more efficient strings. It's the users that should adopt to widespread "standards", instead of requiring every formatting to support every bizzare tag/naming scheme.
But, the following might be a good compromise: For tagging, I think %album artist% should be the one and only, but one user definable "marker" like 'VA - ', would be nice for people that don't like custom tags. When used with Columns UI, the usage in the formatting itself would be pretty much the same as when using %album artist% alone:
In Global:$puts(va_marker,'VA - ')
various=$if2(%album artist%,$if($strstr(%_path%,$get(va_marker)),'Various Artists'))
The first line would be easy to change to suit a particular user in a "config part".
Artist/album column (when using album mode):$if2(%_various%,%artist%)
Title column:$if(%_various%,%artist%' - ')
If this isn't enough, you could always make the contents of the va_marker conditional in case more than one marker is needed (for a given users special needs). E.g. like this (not the best example, but anyway):$puts(va_marker,$if($strstr(%_path%,'-OST-'),'-OST-','VA - '))
I guess that's enough for now...
Edit: nothing important, just added some "air"...
Edit2: I need some coffee. The code for the "artist/album" column isn't that useful, and you'll probably decide it's contents in the global config, and hence you need $puts() $get() as %_various% can be used there.