Thanks for the suggestions. After some mulling, I'm kind of thinking something along these lines:
Dragons, by their nature, were not actually meant to reside on the material plane, instead needing to reside on the elemental planes as they are fueled by the elemental chaos itself. As a result, they have gradually been growing weaker each generation because of their loss of connection to true elemental might (they get some from the material plane, but not enough). At the same time, the lesser mortal races are growing stronger in their weakening state, so it is clear to many dragons looking long range that their time is limited. This results in a number of courses taken. Some are seeking ways to establish a link to the elemental chaos to fuel the dragons but keep the integrity of the material plane (after all it's much more pleasant than the chaos), others are pissed and want to just destroy the plane (if they can't have it, no one can), some leave for the elemental chaos (it's better than slowly withering away), another group is preparing the other races to care for themselves (they've lived under the rule of dragons for so long, they may not be prepared), and most are doing some combination of the above.
At the same time, Tiamat is getting interested and is beginning to do more, attempting to essentially establish a chromatic dragon stronghold (to work out of to overthrow Bahamut). She doesn't do much at first because she doesn't want to get thrashed by the other gods for interfering too much. Likewise, Bahamut is trying to subtly counter her actions as well as encourage the dragons to accept their situation and either leave, or grow weaker. Because of this, the other gods are at the same time kind of "pulling up stakes" and moving away from the plane (recognizing the impending clash and not wanting to get involved). Thus as the campaign progresses, the other deities will eventually have no influence on the land, but the dragon deities will have much more. The only other deities who might stick around would probably Tharizdun or Gruumsh who would probably try to screw things up linking the planes to obliterate the material plane (in fact, I'm somewhat considering that there is no way to safely link them and the dragons who think they can are just being manipulated by this faction).
The ultimate culmination would probably involve fighting one of the deities (depending on who things play out), potentially with the aid of another. Other possible endings would be bailing to a different material plane (in my mind I'm modifying the cosmology slightly so there are other material planes kind of like parallel universes, but only supremely powerful beings like the gods can move between them), or a different "standard" plane, whether or not they helped destroy the first.
Obviously I'm going to cater more towards my players and see what they like and don't once we get started, but any thought? Sound like something that would be fun to play in (of course uncovering what is actually happening slowly and not all at once)?
Also, the reason I ultimately settled on the copper dragon was kind of funny. I was reading through, trying to pick which one and eventually realized that the copper was essentially the "PC" of dragons. Largely good, but does what it wants and tends to screw around and make wisecracks. If it likes something, it will protect it, but it will also savagely attack and mess up anything that looks at it sideways...