For the last few weeks I have been playing with my latest luminosity mask plug-in and finding it useful.
Whilst my previous eq_lum_mask_h_m_s.py is useful when I need to work on a particular, small region of brightness it can be "overkill" for the majority of images. The latest version has only five masked layers, but they are largely independent (two options - hard & soft overlap). Unlike the original luminosity mask plug-in where changes in the dark (D) layer also affects DD and DDD. Similarly for the lights and mediums.

Dependency Python 2.7*.

I hope others will try it and give feedback as to its usefulness and suggest changes and improvements.

Long delay getting back to this
I think both this and your previous script are a good service to photographers, thank you
I understand that Python  has been disabled on linux I wonder if the majority of people though don't use Windows in which case it might be good to use let's encrypt on this forum for more security and to make scripts like this more visible on the search engines
It might be good to have a bit of documentation:
 it's not intuitive to find the right path to the plugin folder on windows
Photographers don't mind having their intelligence insulted when they notice
Be good to have a bit of flexibility and have the options to have the  layer masks as channels; I guess you could use the off-nuts version for this or do a bit of converting
Long time since I did programming but I wonder if it is possible to have a script that updates old scripts using maybe some ' if 'statement and that the original  2.8 scripts could be used to get round the Python issue
 I kind of would prefer scripts to be non-destructive than images
I don't mind destructive images maybe you can blame the Who but we all have different ways of working I don't want to impose mine on anybody
I think Matisse would start a painting again if he felt he had messed up
I tried to avoid working methods that encourage anxiety but I digress
I believe the view if you can talk you can sing and if you can write you can draw so I guess if you can use levels you can use the tone curve as an alternative to getting these effects; that does not stop  it being a valuable service:  the luminosity mask work 
You can of course use them  with the  tone curve
 have a virtual cigar
I didn't test this in a scientific way I like doing watercours as well so find a certain lack of control good for creative work I didn't find anything out of my control that I've found objectionable with this but I haven't thoroughly tested it so I guess people might want to make sure that if they're working JPEG only that they save to xcf before use though this isn't a reflection on the Script rather I've far too much to do at the moment

@Chris_x,

Thanks for your reply and comments.

This plug-in, eq_lum_mask_small.py , and eq_sat_mask_h_m_s.py I created for my own use, but thought that others may find them useful.
To create channels from the masks, right-click on the mask, Mask to Selection, in Select menu - Save to Channel.
If it is something regularly required, I could change the plug-ins to automatically create the channels.

I run GIMP under Linux (Ubuntu 20.04) and I have Python 2.7 (thanks to help from Rich).

My editing is largely non-destructive, because I always duplicate the image at start and at any interesting stage I will do a new-from-visible or save a copy if the process is particularly complicated.

david.

Thanks for this

I was introduced by a community fine art project to gimp so in that context there is something to be said for destructive images a certain lack of control helps

I have heard people using other programs say they get a bit frustrated with the non-destructive

However there are well informed people would like gimp to be more non-destructive and I'm sure they will have good reasons

I understand the sequence of edits can cause degradation and so leaving the program to decide the sequence with non-destructive images might have an advantage

I did some social photography where there was a certain amount of posterization on an edit gave it a good funky look I think it was because of low bit depths and maybe the above
I appreciate you sharing