I would be very interested in playing FE:LH with my friends. I haven't bought the game yet but I have been following the development of the game closely since the beginning and always thought I would buy it one day. As a big fan of MoM and the Civilization series, I would love to play FE:LH with my friends--and my friends would too.
Now, I know Frogboy, Derek, and the whole team decided not to include multiplayer years ago after some pondering. Main reasons were, if I recall correctly, that i) there is supposedly little demand for multiplayer, and ii) it would have drained resources from the single player game design/campaign, mainly due to the big balancing effort required by a PvP game, which may even have spoiled the single play experience.
But I don't care about competitive multiplayer. I enjoy Coop multiplayer a lot more, and so do several of my friends. Enabling Coop multiplayer would require NO balancing. In my understanding, it would be relatively simple to add -- just add a button and some work on synchronic turns as in Civ IV? -- and it would make FH:LE heroes appealing to a larger market, i.e. those like me that value multiplayer a lot. For me it would be the main reason to buy FE:LH. If the AI does not use some good strategy, who cares. We can play 2 vs 3, or 2 vs 4 to make things even, it may even be more fun this way.
So I am wondering if it may actually be worth from a business perspective to enable Coop multiplayer leaving everything else the same as it is now.
ps: And let me also add: I don't care if the game is not balanced for multiplayer even when I play against my friends. We can always decide before we play that a certain race cannot be chosen, or a given hero, or a given unit... I have done it with HoMM and also with Civ IV and had lots of fun playing against them.