Actually it will be the third one, as there are already two released (map pack and quest pack).
As for future expansions I think we'll see one eventually but it may be several years from now. What we know:
1) the Elemental franchise sells well
2) the engine of the game has been limited by 32-bit computers (2gb ram) and old directX versions (bad GPU usage), to the lament of Frogboy and other devs. They've repeatedly said on these forums that a big reason for this was that E:wom used that architecture, and since they "gave away" two FE sequels to early adopters of E:wom they couldn't change the requirements too much. This was going to change in a future game in the franchise.
3) multiplayer is something that they want to do, they have the budget for, but they haven't found the right network genius to work for them. Multiplayer would require a large investment in other areas of the game, which would need rewrites (tactical combat, quests). Multiplayer is an obvious thing to put in a sequel.
4) A reason for moving to Steam was further integration into the Steam platform, including the Workshop for mods. Although this is not set in stone, it shows that they have plans for beyond FE:LH (adding workshop to FE:LH would be too big of a feature at this point).
5) They did a poll on the forums where they asked what people were interested in. They mentioned doing titles like MoM2, new Fall from Heaven title, and another Elemental game. In the thread https://forums.elementalgame.com/439794 they said it was not a case of doing one or another, but rather which they would be doing first. The vote had 60-70% voting for further evolving the Elemental games, rather than other games. This tells them (and us) that their fans want more Elemental games.
