Particularly with elemental being more single player focused the dungeons would be nice, they wouldnt be as practical in a multiplayer game. However I agree that they could be set up either as a random map of connected tiles, or a preset map, or even if your search is abstracted as say 5 tactical 'fights' in a row. there could be non-enemy things to interact with on the tactical screen.
I'd have the multi-play work the same way as the main game, the map can determine the speed (world settings). Id have some option for the tactical battle (and a better auto resolve function). That way the game could be set up to have battles with only one player and the npc monsters/characters move more quickly and the ones with player vs. player or some team up thing run in tactical. All or most of the other stuff should be fine the way it is. Id probably run it as more of a lan set up thing, with just basic matchmaking (probably thru impulse account or their id on the forum), running off of the player's pcs not a server. Geographic location might limit some people with slower connections, but chances are that your not really going to be searching for a random game most of the time but to play with specific people. Though I wouldn't be opposed to some kind of option for open random slots. Might have to limit faction/sov choices to prevent duplicates (probably go by first come first serve) or allow an opportunity to play it with an alternate name and color set (perhaps just grabbing one from an unused faction).
It might run slower as you wait for the other players, but I'd let them worry about that or worry about tweaking things after that point- perhaps recommending adjustment on graphical settings?
Naval/arial combat could be cool but im not sure of the best way to go about it. Perhaps kick to a tactical battle with special tiles (such as if a ship weapon tile is stood on, a unit may activate it for their turn to use ship defenses, and targetable areas such as a mast or rudder that can debuff the opponent if they are taken out. Or sea monsters effectively composed of a few seperate units. A giant squid with say 4 arms that act independently for movement/attack and take up one tile each (targetable monster body optional). Or that could be a tactical battle that takes place a level below a ship vs. ship tactical battle (using the ship/fleet members as the units) with the carried units coming into play when ships are join melee range or use a board option or something).
Some more fantastic elements to the environment/ locations would be nice, we may see some in FE, but right now its like magic based society trying to establish on a world previously uninhabited. There dont seem to be any lost technology or pieces of the past on the map, just wasteland. The goodie huts and nodes help some, but you'd think you could find say a ruined city, instead of a go in and get an item goodie hut, it could do a roll to see what you find (perhaps a limited list of items/tech that are removed from the list after found, but you could still encounter wildlife, raiders, or nothing when you go back- it would also provide a place to build up troop xp. Otherwise it could be visited say 5 times before it is considered explored (some of these could stay on the map after cleared so as to break up the landscape (and would prevent building on it unless you cleared the land).
I'm hoping FE will address some of the modding limits so we have a little more freedom to tweak the game.
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). Imagine your Ogre smiling before he smashes that do-goodie Altarian to BITS! 
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