Some circumstances have arisen in my home campaign which leads me to the idea of seeing some level of cooperation b/n the 'new' Cult of the Dragon (the ones focused on living dragons and summoning Tiamat) and the PotA version of the 4 cults of elemental evil.

In your esteemed opinions, what would be a good way to accomplish that, what might that look like, what sort of wickedness might they get up to, etc?
While the larger cults may simply be supporting one another for their own reasons, I'm wondering if there might be some splinter factions that would form that find a 'dogmatic overlap' between the two cults. Common ground taken to a different level, if you will.
Also, what activities might the two groups have in common?
Finally, where might they fundamentally disagree and, thus, find themselves eventually at odds?

Quote from Jimberish >>

Some circumstances have arisen in my home campaign which leads me to the idea of seeing some level of cooperation b/n the 'new' Cult of the Dragon (the ones focused on living dragons and summoning Tiamat) and the PotA version of the 4 cults of elemental evil.

In your esteemed opinions, what would be a good way to accomplish that, what might that look like, what sort of wickedness might they get up to, etc?
While the larger cults may simply be supporting one another for their own reasons, I'm wondering if there might be some splinter factions that would form that find a 'dogmatic overlap' between the two cults. Common ground taken to a different level, if you will.
Also, what activities might the two groups have in common?
Finally, where might they fundamentally disagree and, thus, find themselves eventually at odds?

 Well, both of them want the beings they worship to be in charge, which might be a point of conflict. But both also believe that the current society is incapable of supporting their needs, so that's a point of overlap. Honestly, all it really boils down to is their core beliefs: What changes do they want to bring about, and how do they plan to make them happen?

Both want to summon powerful beings from alternate dimensions. Both of them want to destroy the current populous and take control of everything. Both need secret hideouts. Really, they're almost exactly the same, except with one having a draconic theme and the other an elemental theme. I'm not sure if they'd ever fight each other, except maybe after they succeed in their goals, at which point Tiamat and the elemental guys they summoned would get in a fight. Until then, they'd probably be pretty good buddies.

Both of them have legitimate fronts, such as a church to a different god or a wealthy merchants guild or a bank, and both of them have succeeded in tricking the other into working with them to achieve their goals. As their initial goals are the same (the subversion of society, bringing about a dependent populace who will serve their deity), they have not clashed. Later on, as they start to find their priorities clashing, they find out about each others actual nature and this pushes them apart and back into conflict.

So, one fronts as a merchant guild and the other as a church. The church approaches the merchant guild to try and tempt them to increase corruption and undermine the current leaders of the kingdom, claiming it's to "put the common folk in charge", meaning the wealthy, which should appeal to merchants. The merchant guild accepts, convinced they are dealing with a church. The church is convinced by their performance that they are dealing with a merchant guild. Neither suspects that the other is a rival cult, and think it fortuitous that they both want the same thing!

Elemental dragon splinter sect. Flaming dragon. Water dragon, much like a leviathan. Purple worm like stone dragon. Blue dragon like air dragon. Scary elemental dragons would make great bosses.