Nice to know that the AI will adapt to mods. I play Single Player a lot. I hope this game manage to have an attractive multiplayer tough, with co-op. I'm sure I'll join this one.
I really think the custom stuff will be somewhat balanced for this game. This will be just a matter of having some different things for your many games, with also different stats/characteristics. Balanced content will have a separated section, and Stardock might test and guarantee the most popular ones. I'm also the kind reluctant to use modification unless balanced. I beleave, many people would use this feature, at least to add 2 spells and 1 cool rare creature for their next game, etc. It's not about changing the whole game (maybe only if picking packs).
I keep in the line when I think if its better to have a world with it's own strong characteristcs very emphased (The creatures that existe in it, what is magical and what not, for it to have its own story and feel unique) or feeling like an open place to put things into. Maybe it will feel has both. I think it will be good to pick a few units/objects/powers to change the experience in bits especially if the matchs are durable (reads: Epic). And also be easy to compreheend with a list of what the chain of productions are. Better yet will be having a list of prefered and balanced cool new additions, and allow the game pick a few of them by random to add to the vanila world, especially if there will be fog, which I beleave will. It might feel like hearing your shuffle music [They are all good but what am I going to get this time?]. I would never change vanila too much, unless there are very well made packs that change the whole thing, for some matchs.
I guess many will use it, if the skins are well reproduced and beliaveble during close up battles. And I hope matchs are durable, so you can remember them like, that "Demon Steeds match" etc. Also from the 'picture' I'm getting that almost everyone will be capable of producing material? I heard it will be similar to Spore uploaded content system somewhere.
[Some people talking about balance, has I see it: For exemple, an unbalanced content can exclude everything else that there are in the world. If Gold Armor sources are abundant why use the Metal Amor, and what will be the valor of the Gold Amor if everyone can have it?. Lets say the Demon Steeds are very powerful and relatively rare to find a group of them, then it can even only have a medium chain of production for it, but its 'resource' or the groups of it, will be very scarce troughout or in very especific habitats and be hard to tamme/train if it gots agressive behavior. But if a channeler (player) appears more close to it or find it, then the game might turn in his favor. Everything needs to be balanced to be fun, and can be, in a way]
Sorry the english mistakes.
EDIT:
Another game that have chains of production and resources. This feature sounds has like is used in the Railroad games where varied resources and animations really adds to the fun. I can't forget for exemple, a game (in SM: Railroad) where I happened to have my start industry in the northeast, a region that were good for grape and had many productions of it (~90% of the avaliability). I happened to be successful there and considered myself the Grape KING, and that was a memorable match to me. Another matchs, the gameplay is intact, but I could transport cattle, gold or cars that had different models, animations and ways to deal with, so the game would feel yet more fresh while mantaining the core gameplay. The more possibilities the better.
Likewise in Elemental, a player can happen to start in the south Icy Regions and beggin to set his cities there. In that game was added a blueish white kind of steed, that happens to live at that habitat. He found 90% of the sources of it there since the map generated only one big polar region. In another region of the map a second player got access to the Demon Steed that live at inospit places; it is more powerful than the Frost Steeds but not has docile or easy to train, meaning access to less numbers and he also only got 30% of its total sourcers. He might look for another source type and mix his army mounts if needed. First player will be known for his characterists of having battalions of men only with the finest Frost Steeds in march in that match. A third player got access to another source of rare Demon Steeds and also magical Forest Bears or Wood Elfs that live there and are willing to help, if you can convince them.
All these were added apart from the vanila ones that everyone already played with to much, and yet balanced to feel like vanila stuff. Vanila were Griphons that habit mountain caves and Hardened Horses but you played with them a lot. This can be changed and balanced just like the Railroad game that can have many different resourcers types with different characteristcs (gold, corn, cattle, grape, cars, iron, passengers, mail, etc, that don't fit into the same match) to give more uniqueness to matchs that will come subsequently. Some almost equaly good, some not so good, some incredible great but scarce or hard to produce. Strategy (what to do, how to do) and some luck (exploring) is what makes the gameplay.
Gold might be the best mineral to make armors, but in another match you can make extremily rare Titanium comes into play, or let the possibility for randomness to emphase exploring even more.
Kind of like Spore ideology too for mods, its not to change the core gameplay like most mods usualy do in other games, its just to add differenciation and variety to it. Vanila gameplay will still be there. This just need to be well implemented and will be a success. At least that is the way I see it and would like; if there is a way to the mod units and spells to feel solid in the simulated battle screen, that'd be amazing imo, but seems complex. It can be player's or company's content, but I liked the variable idea anyway, that is, to add new things in the world to come into play (or change), when they are balanced.