Just keep clicking next turn until you build a swarm of units. Shuffle your swarms of units until they reach the enemy. Hit auto resolve to crush them. Repeat over and over. Nothing could be further from fun than this.
You make some very good points. With this part you mention here though, think about this. What will happen six months after the launch of Elemental and you sit down to play a game? You'll know exactly how everything works and what everything does. You'll know how to auto win every battle you play without losing barely any men. What will stop you from playing the way you just mention above? You'll be able to get through the beginning of the game rapidly to tell how you're empire will go. I do that in Gal Civ quite often. It takes a good 15-20 turns to find out if there are any decent planets near by and whether or not I'll be able to get a "good start" so I know if it's worth going for turn 300 or 500.
Then if the player enjoys mopping up, provide the 'continue' option. Just for fun, if the player continues and actually conquers every single territory, provide an additional victory ending like 'total annihilation' victory sequence or something.
I agree here 100%. I'm hoping they'll have an option to keep playing. Same as you, I think once all the enemy Sovereigns are dead you should win. The only fear here is I don't want it to be easy to get to a enemy Sovereign if he has a huge empire. They definitely need a way to avoid a "Sovereign Hunt" to some extent.
I think it's a given that, whatever the victory conditions may be, there should be a "keep playing" button after victory is achieved for those that want to "mop up". Nothing should be there to stop you if you really want to hunt down each and every last enemy unit and perhaps even fill out the tech tree and develop your civilization further once you've no enemies left - not a playstyle I favor myself, but for those that like the mopping up, go for it.
Really the only thing that's arguable is when we should get that victory screen, for those of us that don't want to get stuck mopping up - obviously no game has gotten this perfect yet, but overall I think the more victory options (options mind you, these would be things you could turn on or off at game setup) the better. Personally I love victory by conquest, but try conquering a truly massive map with dozens of enemies (up to 32!) - by the time you conquer two or three or ten nations and absorb their territories into your own, you're so far beyond any single rival that there's no challenge in continuing, yet you still have hours left of conquering helpless enemies before victory is 'official'. In this situation, even if you love conquest, you might find yourself looking for another option.
As an example of a way to solve this dilemma, I'd love to see a quest that opens up when you've achieved 50% of the world population/territory/or military strength (that is to say, when you're as strong as all your rivals put together). You have a choice, if you accept this quest all remaining rivals will cancel their current wars and ally against you, but if you can then gain control of your strongest enemy's capital and move your sovereign there, or seize an artifact that spawns in enemy hands (or both!), then you can crown yourself "emperor" and your enemies will submit, ending the mop-up. And like anything it'd be purely optional, you could just as easily decline the quest and conquer your enemies the hard way if that suits you. The idea being that this can force a huge, drawn out game into a single decisive lord of the rings-style climax, a battle over a single city or item that decides the fate of the entire world - if you want it to.
Edit: just for fun, lore that would justify the above quest. Your minions have found, in the ruins of a recently conquered city, an ancient crown once worn by a king that (legends say) ruled the world from his throne in the city of [strongest enemy's capital] in a golden age long ago. If you choose to wear this crown, your enemies will know you seek to repeat this ancient empire's dominance of the world and ally to resist you to the last. If you are able to overcome their forces to capture [city mentioned above] and seat your sovereign upon its throne, your enemies will be forced to obey their ancient oaths and swear their loyalty to you, the new king. Alternately you can forget you ever found this crown, discard it before your enemies hear that it has been found, and continue the game as normal.
I agree 100% here as well. I particularly like the quest idea you give towards the end. I'd like to see exactly what you suggest as a stage of the campaign. This should definitely be a "mode" of play to select from.
Some mop up is fun. It's nice to see the momentum swing your way after 'the turning point' and you can pay back some past greivances. After a point thought, it can get tedious.
One thing I would like to bring up is there may be ways to make the inevitability of the Win less predictable and thus make mop up less boring. It would be interesting if there were several avenues of magic research or quests available to losing realms that lead to unpredictable results... last chance forbidden magics, so to speak. Something that the winning realms wouldn't want to do due to negative effects but losing realms have less to lose. These should have a high chance of hurting the losing realm itself but have some global effects that affect everyone or element of randomness. For instance, something that unleashes vortexes that randomly move across the land. Turn an army into powerful undead who die after 10 turns. Obviously, a lot of thought would need to be put into balancing this

.
Also, this type of option would be nice if *I* were playing the 7th ranking realm of 8 realms and want to play with some chaos magics out of despair.
That's an Awesome idea as well. An idea that comes to my mind is a losing kingdom deciding to open a door to the underworld to make a deal with a demon. There's a chance the Demon ends up going to war For the kingdom that set it free. Or, there's a chance the Demon goes to war On the kingdom that summoned it. After it destroys them it sets about rampaging the lands until some army or hero put it down and send it back to hell.