Oh, yeah I have my own list that I use, and I agree that compromises have to be made on lists like this because you could easily end up with things that straddle two completely different genres that aren't even remotely related on a genre/subgenre scale haha.
That's a great list and some very good suggestions.
It looks like I will be adding at least a few of them.
One thing I will need to look at and digest a bit first, is if (non metal heads, average users) would consider each and every one as a specific genre, and/or if it is useful and practical to have separate entries for each of them.
Words such as 'progressive', 'melodic', 'industrial', 'symphonic' are often a description of style or form, and not always a clean cut genre or sub-genre.
If they, and all variations would be used here as specific genres for metal, other genres would probably need the same treatment.
And then my aim for having a maintainable and practical list that is not overly convoluted will probably be too much compromised.
As a very extreme and exaggerated simplified example; you could have only 'metal' as a genre, and put all such descriptive words in a separate keywords or form/style tagging list, and use them as a filtering method. It sounds crude and simple, but it could work if you would get used to it.
So, again decisions/compromises will need to be made here ;-)
I would treat Blues as part of R&B, or its own category, personally. At least in the US there's a certain implicit idea that folk (and country) is "white people's music" and Blues/R&B is "Black people's music". I'm not saying that's right, but it's a thing. I mean, the early billboard charts called African American music "race records", before switching to "R&B" around 1949.
Glancing through your chart now, I question Industrial as a separate category. Most of what I know of as Industrial would fall under Electronic or EDM (I'm not sure about EDM as a separate category from Electronic, either... but this is why I dislike genres!)
I am looking to get rid of the 'American Folk Music' genre category. It has some issues that I think can only be resolved by having some extra categories, and indeed Blues probably is going to be one of them.
Black vs. white music is something that in my opinion is impossible to use as a factor in such a genre list.
Even when looking at traditional folk music, there is usually so much cross-polution in the origins of it, often having influences from both African and European countries, that while the colour of a skin is relevant in cultural music history, music labels, theaters, and radio, I don't see how it could fit in in a sheet like this.
'Industrial' was and is a difficult one indeed.
It can be a descriptive keyword, and it can be tied to a genre.
E.g. 'Industrial Rock' and 'Industrial Techno' could be considered specific genres. And, one nicely fits under Rock, the other one under EDM.
But I had the impression that at least in the beginning of the 'movement', there was also Industrial music that could not be placed under either classical, rock, electronic, etc.
I'll see if there is enough (or even some at all) of that music available these days. If not I may be removing the category indeed.