Beta has to make the right balance, sure; but I doubt if it is possible from the feature info we receive from them so far. The game will then always evolve to hunt/defend the channeler every time; this is boring yet the most effective way to play the game.
That's narrow-minded. Neither you nor I nor even the devs really know how the game will turn out, let alone that it will always evolve to hunt/defend the channeler every time. If done well, channelers should be very adept at getting out of fairly sticky situations. It should also be possible to set up safety nets so that if your channeler is trapped and outmatched, you don't lose upon death. Whether the safety net is in the form of some passive spell that teleports the channeler away at the last instant, resurrects him, whatever - and whether it's achieved through a spell, a magical item, a building - whatever.
The one thing I personally don't want to see being able to continue to play if I lose my sovereign without having created any sort of safety net. And I am opposed to any kind of heir system, as well. In Elemental you take on the role of the sovereign, and as such deal with matters of state, logistics, combat, magic, and so on. But you are the Sovereign (not the state itself), and if you the Sovereign die for keeps, you should lose. I don't like the idea of hopping over and inhabiting another character just for the sake of being able to keep playing.
But back to my original point, there are many things that can prevent the game from degenerating into a game of chicken, all else falling to the wayside. Quite frankly I think SD = GO would add quite a bit of strategy. There's the question about whether or not to create a safety net, and if so what kind? When do you send your sovereign out into the world? Do you send him covertly, or as part of a massive army? When invading (or defending) do you risk taking massive losses in a bid to knock out the enemy channeler early? Or do you try to whittle down your opponent's forces until you can catch the channeler relatively poorly defended? Even then, would the losses incurred by taking out that channeler be worthwhile when instead you might be able to negotiate very favorable cease-fire conditions?
Sure, if the channeler is some pansy unit that can't defend itself, sovereign hunting will be a sizable part of the game, even though most people would just park their sovereigns in a city somewhere. If sovereigns are so weak it would be pretty easy to mobilize a small but sufficient strike force to overrun and kill them. But in Elemental, channelers are supposed to be beasts capable of single-handedly crushing small armies (at least as one route). If you want to successfully ambush a sovereign, you had best bring a quality army, and expect heavy losses. As a result, going after sovereigns will be slightly less appealing, and it will be easier for sovereigns to escape. Big armies tend to move slower than small strike forces, and mobilizing such an army at a moment's notice isn't so easy.
Somewhat related, I want there to be an ability/spell/option for sovereigns to 'blend in.' It would be neat if, for a cost (perhaps the city gains a smaller bonus from your sovereign's presence, etc), enemies can't tell whether or not your sovereign is in a city, unless they have intel (whether traditional or magical).
Edit: With regards to aging: it can be a pain in the ass for your heroes/generals/whatever that you have slaved over for days to just keel over and die on turn. At first that really bothered me, but then I learned to not mind; I realized it just requires a different manner of play. I'm used to leveling up my heroes indefinitely, making them stronger and stronger ad infinitum. New heroes get pushed to the wayside because they will likely never catch up to my veterans. Aging (and age-related death) encourages you to be more well-rounded. It's tempting to always use your veterans for everything (because they will do the job better!) but if you do that, then when that generation dies you're left significantly weakened. So instead, it's better to use your veterans for the truly important (and close) battles, and use your rookies for more minor battles, so that when one of your old veterans dies there is someone to replace him.
On the other hand, a big problem with age-related death is randomness. Your 60 year old general might die next turn, or he might die 50 turns from now. While unexpected death does happen, it is more common for someone's mental and/or physical health to decline to a point where they either retire or are made to retire, well before they actually kick the bucket. Basically, I think for age-related death to really work, there would have to be a way to monitor hero 'health,' and for that to actually affect their performance. That way, you are basically nearly always induced to retire aged heroes before running into the gambling issue above. And I'm not sure age-related death is worth all that.
