I have some functions to hopefully address a useful subset of these "layer and setting related" requirements in a development branch now - note that the naming of stuff is likely to change.
My design philosophy is that new users will not need to look into these capabilities as they really have value when dealing with more elaborate layouts and needs. And so I am hoping those power users who do need this are "up" for a little setup work on their own part to enable them to be delivered much more quickly.
Here's what is in the dev branch -
1. A layer can have its layer show/hide button on the main window hidden (not included in the button list - the number is "skipped", the layer can still be selected in the droplist, however).
2. A layer can specify a list of other layers that will be hidden/shown when it is hidden/shown. Note - the layers in the lists do not have to be unique. They are single level (the other layers do not cascade show/hidden).
-> The intent of these two items is to allow groups of layers that are associated with "master layer" buttons. The masters could be by layout level, or by gauge, or all sensors, for example. In fact however the user chooses to use them.
3. A layer can specify a settings file (new format .xset) in the working directory that will be read whenever it becomes the current layer and override the settings within it. If the settings file name is blank, the current "default" settings will be re-loaded.
4. Saved settings files are able to be created (and loaded manually) in the Layout Options page. They are a named copy of all the then current settings put into a settings file.
Because the settings files are in text format, and the records are being documented in the wiki, they are human-readable and can be easily edited by power-users using a text editor. Only included settings are set. So a user could choose to remove all but the settings they care to change for the layer(s) in the named settings file and so only override the scale, or scale and colors, for example, as suits them.
We already have the ability to save/load the layers "setup" - and some power users already know they can copy, edit and replace these in the (single) settings file, so that they can easily define all the layer characteristics using text editing.
While I appreciate the UI aspect of a combolist with all modifiable settings in that list would be preferable - but extending the UI for more than two objects per line in combolists to cover both Windows and GTK is a heavy lift and certainly not achievable anytime quickly. So I hope the ability to edit the configs outside the program will somewhat compensate for this.
I also know that having UI control over what is stored in the settings files would be smoother, but I am hoping that by allowing user control, in a "UI tweaks" manner, we get a faster functional delivery - and some bright person could always create a settings tool outside XTrackCAD to display, modify, archive, the settings.
Anyway, that's what I have, questions, observations, brickbats, etc.