I really don't get this need for modularity and as you I don't really think that the CPP audience would get any bigger if I actually brought such feature.
But for a project like this it doesn't make a sense. Why would anyone not want to install spell fixes? CPP is unlike EMS not a hak, it does not overwrite your scripts - if you have all spellscripts changed nothing will happen. This is also not hitting any limits like PRC with too many classes from half of them are bugged or CEP with 16k resources issue, DM crashing and overally slow initial game loading. If there would be such issue, I would understand the need for modularity, but there simply isn't.
Also where would that end? Currently CPP consists of over 4k various fixes and only per category there would be over 20 of them, and would that even be enough? I do think that even if I did this, it wouldn't be enough till there was possible to select specific file or specific fix in the file (in case of includes for example some of them have over 100 different fixes in there)
NWNX_Patch and NWNCX_Patch are basically standalone, even that there are 2das and scripts in CPP that are needed, it will work without them. This content attracted several builders already, unfortunately, all of them were only interested in source - took away what they didn't have yet to their own plugins and gave nothing back.
Imo, module switches are already providing enough modularity. I said it many times already and Im saying this again, an usual builder should not even notice anything has changed after installing CPP. Yes some things might happen especially if you won't merge 2das but even these issues are now fixes in 1.72 so they won't happen again once 1.72 will be released.
Im wlling to consider to make colored icons modular, on the other hand - those who require/criticize not enough modularity are builders who doesnt even notice there are colored icons as thats content aimed for (new to the NWN) players only. Those working on a module will see it probably only if they go test something with F9.
Anyway the problem with making anything modular is that the BIFs are not modular. CPP is unique project as it uses BIF files, but there is no way to put content into BIFS dynamically, the whol BIF which as now 150mb is packed as is in the installation. So if colored icons should have been modular, they would need to be added as an override. Which would then replaced already existing icons in override directory if player wouldnt paid enough attention and didnt unchecked that option in installer. Also there are class, skill, spell, emote and other icons and then it would be "we want each icon category to be module" again I bet. So I don't think its a good idea afterall. The current method of automatically adding colored icons and tell those who doesnt like them to download restoration pack is not ideal but I believe that its not ideal only for a minority of CPP users. Okay there were probably some players who installed, didn't like icons and uninstalled whole CPP but at least they tried, the only ones who I've heard are not installing CPP because of icons were again builders which is bogus anyway.