Nerfing summons makes sense, as does the overall change to mana.  However, can we expect significant other changes to the spells themselves?  The non-summon spells need more power and, most important, variety.  It's important to balance spellcasting, but you also need to make it less boring.  Insert inevitable MOM reference here.

Have you considered limiting the number of champions to for example <1 + Number of Controlled Shards> That would reduce the "Imbue every champion I can get my hands on" issue.

And perhaps limit the level of spells a character is able to cast to it's own level so a level 1 character can only cast level 1 spells, but a level 7 character can cast all spells up to level 7. This would reduce the problem of human players rushing to research a powerful spell and using it to crush the AI, since they would first need to get their spellcaster to a level where they can cast the spell.

The mana pool is a good idea, all these concepts sound like the Age of Wonders system: with "shards" instead than "nodes" but that definitely works so I have no problem with it.

Still you have a few overpowered units in the game. The "spy" for example can be devastating: it can inflict 20 points of damage per turn on turn one to every single enemy units. Make an army of them and nobody will be able to survive turn 1 of any attack.

Regarding the AI, I followed the way AOW evolved, they tried different things and in the end I believe the best tactics for sovreigns is to stay inside their capital, not just next to it: but INSIDE. In this game if the sovreign is close to his city the city can be taken making that instantly an enemy territory (by saving and reloading the turn at the moment). The sovreign can then immediately be attacked and killed, game over for them. Also I am perplexed that the sovreign cities disappear once he is gone.

I believe all those armies and cities should become hostile and aggressive against the player. Call them "neutral" cities or "rebels" but they can just keep the flags and insignias of their former affiliation even though their faction is dead. You don't even have to change their look in fact. (Notice that in Age of Wonders Shadow Magic that's the way it works, only in that system the sovreign once killed respawns only inside his tower assuming he has one. With this system in EWOM the enemy ruler would be much harder to kill making this game more challenging than AOWSM since a sovreign who stays in his city becomes virtually impossible to kill until he has cities to respawn to... But maybe not all sovreigns should be pursuing such strategy...) - Also the AI should become extremely aggressive with players who are pursuing an expansionistic strategy (after they have killed several sovreigns).

In most games of this sort when you conquer an enemy city you better keep an army in it or the population will revolt. In some games even creating armies out of the blue (Total War) - That slows down the advance in enemy territory in a realistic way since some troops have to be left behind.

The tech trees should be IMO related each to a specific resource: Imperium=Food  - Sorcery=mana - Domination=Gold, so that each of them would have to be researched (it's already a bit like that but it could be enhanced)

Regarding the combat system take a look at Heroes of M&M, there are great ideas there, and I would suggest to make bows and certain spells more or less powerful according to the DISTANCE from the target. Also I would speed up the animations, but that is obvious.

Mana regeneration is more important than the total essence. The tower of magic should speed up mana regeneration, not give lots of essence which I will never be able to reload anyway.

Do we really need diplomatic capital points? I always use them to buy whatever I want from the enemy before killing them off. If I am pursuing a non diplomatic strategy they are just a big exploit

....An please most of all GET RID OF ALL TELEPORTING SPELLS!!!! They spoil the game making the beautiful geography of the map completely useless and making all games be the same with just a super stack jumping around (teleport is a SCI FI device not a fantasy one!!!)

Hopefully we'll be able to get a Play By E Mail system some times, since I doubt multyplayer LAN will be very popular in a game that takes so long to complete. After all PBEM is what keeps Age Of Wonders alive after all these years.

A couple of thoughts I have after reading this.  Certainly interested in how it shapes up over all, but some concerns:

1) Champions need to be more useful when they show up.  All champions show up with minimal or 0 gear, even higher level 'adventurers'.  This makes them virtually useless in a fight.  Right now I can make them useful by imbuing them.  Unless I'm deep into the warfare tech tree I can't equip them with weapons/armor that help them match up favorably with anything beyond basic monsters.  Later when golems, shrills, etc start showing up my champions get shredded.

2) Related to above and mentioned earlier in the thread, they need to fix it so that champions with special abilities can use them even if they aren't essence-imbued

3) There needs to be more to the mana regen than what is described above.  As written, if I have my sov and beginning shard, I can have 1 imbued champion and 1 summon, and then net mana regen is 0.  So if I can any otherspell, I use some up but can't regen it back.  Obvious solutions; Buildings that boost mana regen, sovereign skill that boosts mana regen that we can level up instead of leveling up essence, mana regen items, etc.

Overall, I'm actually relatively happy with the current magic system.  There are some balance tweaks needed to be sure, but I can make up for the low rate of regen right now by imbuing champions.  That way I can win battles with magic by sharing the casting load across multiple units and not deplete any single caster too much.  I want to be able to keep using magic to decisively turn battles in a game like this and I'm worried that the coming changes will prevent that.

This

If things are well balanced a level 3 summoned unit should be roughly 3 times as powerful as a level 1 unit, therefore it should cost three times more to cast and upkeep.. Unless a specific unit was conceived as being advanced not for its intrinsic power but for its cheap upkeep...

I don't like the idea of spellcasting champions having a mana upkeep. At least allow this to be an option. Now I do like the Summon creature upkeep cost.

A General Purpose CPU can solve an O(N^3) problem much more effortlessly (and especially through brute force methods) than any human being can.

I cannot state the same for an NP-Hard.

I agree with Storm's Statement as it being only half the AI problem as well.

Adding Patches that make nonsence out of the tech trees is not helping... (Proof: Look at Kingdom Maces and then Warhammers... )

 It could be successfully argued that much that society claims as Science Fiction is a a subset of fantasy so I agree that Teleport should stay and I like the larger Mana cost to reduce how often it is relied upon. 

same here! right now the AI lacks the basics, like not sending only melee units against a wall of arrows about 10 times in a row...

about moving, why the heck a horse/wolf only gives 1 more move point... the same as a pair of boots or a special cloak?