Just on the thought of the Sovereign being replaced. Personally I Like that. A LOT.
That having been said, I can also see others who want to play a near immortal sovereign who sires a great lineage and remains married.
But for me.. I want the sovereign to pass after a time so he can then pass his "Power" down the line to the next worthy heir, irregardless of gender. Who then continues to pass down the power throughout the generations. To me, that would be frakkin' toasterific awesomesauce.
I was thinking something potentially along the lines of what they have in the more recent Total War games where your sovereign marries has and has kids.
In regards to Elemental, you get to chose your spouse (in TW, you get whatever spouse your king, etc managed to find on their own when you aren't playing puppet master 
).The children of your king age and then eventually mature and become general's that you can send around the map to lead armies etc. They can in turn marry and produce their own offspring which will perpetuate the cycle. Typically there is a designated heir based on the european model of first born son, etc.
I don't profess to be a scholar of Elemental's Lore (actually I don't know much besides the basics) nor do I currently have access to any of the Beta builds, but I would recommend that sovereign's children either inherit their parent (sovreign)'s ability as a channeler either as a equal state, or some form of weaker state (their blood has been diluted by a none channeler's genetic material (spouse of sovereign).The weaker state may be harder to implement (how to reduce spell efficacy, etc.) in addition to leading to potential more weakening issues if the children mate and produce additional offspring. This could be implemented as the penalty for getting your sovereign killed off, while not completely bringing your game to a crashing halt.
It would be interesting if you could utilize your sovereign's children as diplomatic trade chits to so speak to cement diplomatic ties with another empire/kingdom through marriage, but this may be getting too in-depth, and Stardock may not want to implement too many ideas that "borrow/copy" from another game.
I believe this would add a dynamic facet to the game. (sorry for my rambling post, I just let it all come out free form).
