If you do not think it will be RPG or Civ-builder (the two main themes of FFH) then what do you think it would be?
When I said Mount and Blade meets Suikoden, well, Mount and Blade is completely free-form and Suikoden has some flexibility (especially w/ merchant trade) within a tight storyline. What I was thinking was to still have a storyline, but to have many more branching paths ... as a "pick your adventure" RPG, where instead of tiny outcomes to your crossroads decisions they are HUGE impacts to the outcome of your story. And to have more of such crossroads.
For instance, the Malakim hire you on as a Mercenary, and you show great promise. Then an agent appears to you during the night asking if you wish to join Mahala's Campaign. A royal courier approaches your station during the next day and asks for your aid in Capria's Campaign.
If you take the Doviello campaign, you play the Dov storyline a bit and then during one night a Sidar assassin attempts to kill you. Then you are approached by a Shieam emissary, and you can either choose to completely betray the Doviello for the Shieam, or you can convince the two nations to work together for a time.
If you choose for the two to work together, then after defeating opponent X (lets say a major Sidar city) there is turmoil between the armies. At this point you need to fully side with either the Shieam or the Doviello. If you side with the Shieam then you have the choice of learning the Dark arts of either Magics or the Spiritual Veil. If you side with the Doviello then you are given a position of command, with a number of warriors immediately at your disposal, and you may train yourself with specialist bezerker abilities.
If you choose the Doviello, then you will later find yourself on a campaign against the Bannor. If you side with the Shieam, then you will find yourself fighting against the Elohim and later summoning the Infernals. An infernal imp will meet you in the night. If you decided to follow the veil, then you will be given the option to enter hell (at Aeron's level) to train yourself as a demon lord. If not, then you will still be offered a position of command on Erebus leading Infernal demons. You will also have the choice of remaining with the shieam while supplying the Infernals with necessary information.
If you choose Shieam, you will be invaded by Hippus, Bannor, and Lanun. If you choose Infernals, you will be invaded by Malakim, Bannor, and Mercurians. If you choose hell, then you will go through the trials of hell to eventually emerge as a demon lord under Hyborem's command.
If you choose the demon lord path, then the Infernals will have already slaughtered the Malakim and Bannor invasions, while the Mercurian army has grown vast beyond number. your main fight will be with the Mercurians.
If you choose to be a mortal commander of INfernal demons, your main campaign will be against the coalition: with one section dedicated to fighting the Malakim, and another section dedicated to a combined bannor/mercurian force.
If you choose Shieam, after you defeat the mortal forces aligned against you, you will set sail to aid your Infernal "friends" and have your main campaign be against the Malakim.
After largely defeating the enemy (with either path of Shieam/Infernal), a massive army of demons and men led by Keelyn will arrive. If you are a demon lord, you will have the option of either following Hyborem or Keelyn. And if you choose Keelyn (as a demon lord) you will have the option of being mind dominated by her (game over) or rebel against her forces and face an uphill battle until she is destroyed. Once that happens, you take command over all the demons.
If you are fighting against Keelyn, once you kill her you gain the ability to bend demons to your own will. After this happens, you get to decide the ruler over all demons: Hyborem, Os-Gabella/Tebryn, or yourself. Picking yourself is the hardest option. There is also an option to continue the Shieam/Infernal alliance. If this is picked, there will eventually be a later decision to fully back one or the other (although both armies will still be integrated, it will only affect political rule, not military units).
If you pick either Hyborem or yourself, the Shieam leaders will eventually flee and return to their primary nation, biding their time in wait (and later appearing with the Messhaber of Dis and a can full of vengeance).
If you pick the Sheiam, then you must slay Hyborem and gain control of his demons. Keeping the demon gates open, and gaining the alligiance of the demon lords. Well, those you didn't kill anyways.
If you pick yourself, you will start with a small force of elite demons from Keelyn's and Hyborem's forces, and must dominate/recruit your way into a massive army while constantly under attack by Infernal and Shieam forces. Dominating the undead/zombies is much harder but not impossible.
even though dominating is difficult, you don't lose the ability upon failure.
Either way, once all opposition is cleared (and a leader of the demons is chosen) a campaign will be lead into the mainland, against heavy mortal opposition (and a second (or third) mercurian gate). Depending on your choice earlier, the campaigns will be fairly different. In the Hyborem campaign, you will take out the Elohim first, and gain access to vampire allies. In the Shieam campaign you will take out the Malakim first and have optional access to Esus/Veil assassin allies, demon-worshipping rogues from the nations of Sidar, Svartalphar, and Amurites. (so better assassins).
If you yourself are leading the campaign, you will have far more choices (on who to attack and when) as well as access to all manner of allies. While the customization makes things relatively easier, it will once again be "harder" due to opposition from both Mortals, Mercurians, AND when the Shieam arrive they will be backed by demon lords still loyal to Hyborem.
The mainland campaign will be fairly long and bloody, and you will have to stop a nation from completing the Altar of Luannotar (grigori?) and stop a nation from completing the Tower of Mastery (Amurites?). If your on the Shieam campaign, the Shieam will steal the plans for the Tower, and be able create their own tower of mastery.
If you choose the Tower of Mastery option (as the Shieam) your final steps will be defending the tower from two main armies. A recovered Hyborem leading various demons and mortals on one side, and a recovered Basium leading various angels and mortals on the other side.
And once you win, there will be an evil ending (customized by choices), a good ending (customized by choices), an elven ending (Svart or Ljos), a Mercenary ending (Lanun and/or Hippus), an Auric ending (with either Auric or you becoming a god of ice?), and a Sidar ending. Also, a Tower of Mastery ending (either Shieam branched from evil path, or Amurites branched from good path), and an Altar of Luannotar ending (branched from good-conquest path). All endings other than Tower of Mastery or Altar of Luannotar must destroy the Altar and the two Towers. Alternatively, there might be a possible set of choices allowing you to take control of the Tower/Altar instead of destroying them, allowing for a customized Tower or Altar ending ... although perhaps make it hard enough (must make a very particular path, as well as a certain amount of skills at X level) as to not be a common available choice.
With the Sidar arc, I'm thinking that after you assassinate all leaders with fates destined to destroy the world, you get a false "good ending", and then the game resumes with Laroth invading erebus as a God of Death? In which case, you have a very hard hitting campaign, and eventually (if your able to slay/imprison/etc the god of death) the ending can be for you to either allow the Sphere of Death to remain without a god, or for you to take that sphere and retire in the Netherworld as the God of Death.