I don't usually do multiplayer in games that are expected to last more than 20 minutes, but I'd like to put forth a multiplayer idea for Elemental that even I might try: within the single-player game, for close tactical match-ups, have an option to bring in a human player to play the AI side, provided both armies are large enough for a substantive experience.

Here's how it could work.  While playing Elemental single player you would have the option to go on standby multiplayer.  When you enter into a tactical battle, if the AI side is stronger, or similarly strong, it will search for other standby Elemental players and ask them if they want to take a break from their game and play the AI army in your game.  Of course they could say no and the game would look for somebody else, for a minute or so, and if no one is there, you'd fight against the AI as usual.  Similarly, if you are on standby mode, you have the option to play in other peoples games.  (To avoid sandbagging I'd give each side 20 seconds per turn, and if they take no action then the AI steps in.)

If you lose a fight to a better player, it is no worse than losing any other tactical battle, and you can still recover from it and win overall.

The game would need to have special rewards it hands out to the winner if you are fighting another human, like particularly strong items and equipment you can win, and maybe even consolation prizes for the loser to encourage people to participate.

It would be the sort of thing that is optional but might attract people to multiplayer, particularly if you don't want to commit several hours to a multiplayer match.  It would be a way to learn better tactics by losing to better players and seeing what they do.  It would also offer moments of community play in a generally single player experience.