Something that irked me about Birthright, to the point that I had edited it out of my memory until I reread it last night, is the way they handled their gods. The big event that establishes the setting’s status quo is a legendary battle in which all the gods die and their divine essence flows out and into the mortals present at their demise. This is a pretty cool premise.
However, the lion’s share of said divine essence flowed directly into each god’s most favored lieutenant, turning them into gods. And basically the same gods. This is kinda lame.
It would be niftier, to my tastes, had they done something Unknown Armies-style, wherein a regent who enhances his or her bloodline sufficiently could ascend to divine status, possibly displacing the current holder of that status. (Among other things, it would add some depth to the quest to enhance one’s bloodline.)
Alternately, they could have gone totally hardcore and had no gods remaining, with clerics worshipping the most powerful regents and deriving their powers from them.
Then it occurred to me that Dark Sun was set up a little like that, with its templars who draw magic power from the sorceror-kings. Somewhere out there, someone has run a Birthright/Dark Sun crossover. I bet it was awesome.