Wait, you're gonna add inbuilt compatibility with another mod?
What is this? Who are you and what did you do with LastSword?!
It happens to me that I forget that people know less than me about coding. Maybe I should address a few lines about this little cancer-hitler called external support.
In general, mods are created by such variety of random people that any kind of global compability is illusion, every mod's user should focus on their own yard. Yield changes cause incompatibilities, imagine some ".lua" replacing mods. Tons of things can go wrong, after all mods are created by... amateurs/hobbyists.
None of the custom civ modder is supporting significant amount of mods, nor this is possible, because that's not the way. You don't move hundreds objects for one.
It is much easier and more polite (you don't want to create unneeded incompatibility, do you?) to code your mod that way that it doesn't need a support by default. It is simply achieved by using algorithms in most cases (of course, direct support can be available to let somebody to point the certain values for example).
There are mods that add some non-gameplay stuff, let's take Historical Religions since this is probably first mod I recall about support. Take in mind, that support is mandatory, it will not disturb your game in any way. The support is about assigning the most proper religion to civilization. That's it. Not so scary, one little update to your little civ... Yes, but doors are either open or locked, they cannot be slightly opened. Several mods like this, hundreds of updates/downloads/uploads, and then new mods like this. In this case no algorithm can help (non-gameplay database stuff - I don't like database coding for the lack of flexibility). Let's say author adds new religions, which one is even more fitting to your little civ than the last one.

Update. I don't know, but it may be more user-friendly to update the Historical Religions once half-year, add references to new civs/update if added new religions.
Because who is obligated to support the mod in this case, the mod author or custom civs' authors? Simply answer, nobody.
Let's take a Mussolini of "support" mods, those were maps by Gedemon iirc. True Start Location or something like that. It wasn't designed in mind for custom civs, I understand that (and my mods aren't designed for those maps neither). From what I know, you can't even see a civ that is not supporting this mod (I wonder if this is a reason of some poor steamers that cannot see my civs

). What you have to add? The coordinates (two integers) and some luxury resource reference (which seems to connect to existing civilization...). Wooow, like it is not possible to choose random luxuries (or even connect with the civ from ArtDefineTag) and the same with coordinates (spawn Khmer on Siam spot, or if Siam is taken, find the nearest valid one, after all there is a great table of coordinates defined just for vanilla civs.
Maybe, It is my bad, that I didn't bother to point it out/code it back, show the better way of support, though I don't truely care. Anyway, around that times It somehow people started to support mods externally (aka the burden of support was lied on custom civs makers or they picked it by their own). Anyway, good luck supporting every new mod (thankfully the modding scene is quite stagnant, but still...).
I have noticed recently that for example JFD's created some new "external support" mods in addition to his old Cultural Diversity and Piety. Would I have to update 50 civs again? Plenty of mod's users are gonna download stuff again and again.
Sisyphus's works.
Cultural Diversity is by default assigning civ to Colonial group (culture - Colonial? well, nevermind). It's ok, I suggested some day to make it based on ArtDefineTag (which would support my Polands by default), because I felt sorry that he had update this mod to support some of my new civs - I don't like updating

. That method would probably be a much better than default Colonial group, because 1) some cases would be valid, 2) more variety.
Piety needs like one silly number, a "custom flavour", default to 0 ~ not supported AI civs are gonna ignore it. Unfortunately, I cannot tell how important it is, but in this case you have about 50 vanilla flavours to make an algorithm assigning 0-12 to your custom flavour.
In general, you can quite nicely cover stuff. Civ 4 traits? Read flavours, building class of unique building (barracks? Militaristic) to auto-assign fitting traits.
Too long, don't write. One last thing is that all this external support is making it hard for newcomers, it is quite repelling.
I have no idea how author of Randomized Unique Traits could make it work with my mods, simply because
I have coded them incorrectly/lazy. And let's be honest, this wouldn't be enough for me to update 16 mods if I had no desire to actually play some games with it. My break will be over sooner or later. Yaa, unless unexcepted and bug-free Civ VI appears.
So you see little Hoopie, I support liberty and freedom only.
What is important, I received an art from Kujarim_Wuniver and thanks to Whoward's utility stuff I am gonna update set I much quicker than I excepted. That's good moment to suggest music for Khmer, Hetmanate and Haida. Thanks.