Ah-ha! A minor break-through in my life. I have now put my folders into the following structure
[Area of Life] then a dash then [GTD list name]... } all in the directory name.
So I have folders with the following names in the root directory:
/WORK - DO ASAP/
/WORK - DO, BUT NOT YET/
/WORK - SOMEDAY MAYBE/
/PERSONAL ADMIN - DO ASAP/
/PERSONAL ADMIN - DO, BUT NOT YET/
/PERSONAL ADMIN - SOMEDAY MAYBE/
/RECREATION - DO ASAP/
/RECREATION - DO, BUT NOT YET/
/RECREATION - SOMEDAY MAYBE/
And then – here's the clever bit – I create views filtered by the advanced filter: Foldername contains [list name]
e.g.
A view with: Foldername contains 'DO ASAP'
A view with: Foldername contains 'NOT YET'
A view with: Foldername contains 'SOMEDAY'
The result is that I get to see each list separately
e.g. When I look at my "DO ASAP" view, I see a nice simple view of each Area of Life, *just* showing the "DO ASAP" lists, grouped by Area of Life.
i.e. All I now see is:
/WORK - DO ASAP/
/PERSONAL ADMIN - DO ASAP/
i.e. I can easily open each folder in turn - which I move between simply by using the up/down/left/right arrow keys on the keyboard, and I will not even SEE the other lists (e.g. NOT YET and SOMEDAY)
Also when it come to moving a project or task between GTD lists, that's fairly easy too: I just go Control/M and put it into the desired directory - which shouldn't be too far away.
I still say it would better to have an actual MLO database field for "Area of Life" and another "GTD list", but the above makes it moderately easy to change GTD List (or even change Area of Life).
J