The devs tried this late in the game by making it for sale, but it sounds like they got a bad deal from their distributor, they also sold extra slots, but by that time I think it was pretty much too late.
As far as I understand, their original plan was to distribute online only. When it became obvious that wouldn't pay the bills, they tried the traditional publisher route, but ended up with a bad one.
Extra slots, if I remember correctly, were always part of the plan.
The main problem for Dawnspire was marketing. They didn't have enough muscle to market the game properly and later on their publisher wasn't interested enough to spend some serious marketing money (and probably not big enough to do it, either).
So if this hypothetical Dawnspire 2 was ever built, the marketing should be planned carefully. For small indie games, marketing is typically a much bigger problem than developing the actual game.
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Some comments about the actual brief:
The game will ship with 9 character classes each with between 16 and 20 skills.
That is 144 - 200 skills total, unless classes share some skills.
This would have a real danger of what I call "the Guild Wars problem". GW has too many skills, which makes it really hard and long to learn for new players, especially the GvG side, where it is essential to know at least all the basic builds and such.
They've actually cut the number of skills they are offering back for GW2, which I think is a smart choice. Less skills, but more interesting skills. More difference between the skills, instead of having a couple of hundred clones of "do direct damage" and "do damage over time" skills. Deeper skills, with interesting inter-class skill combinations (just like Dawnspire). Better balanced skills.
So before going with "yeah, lets have gazillion skills", think why you want to have them all? Do they serve a unique purpose? Are they fun? Do they combine in interesting ways with other skills of the class and with skills of the other classes? Are you prepared to spend all the content development budget to do all the assets for the skills? I mean even if each skill uses only a simple particle system and some code, that's 200 particle systems right there. Of course you can get quite far by just changing colors, particle sizes and such, but still.
There was a good reason why original dawnspire released with 4 classes and 7 skills each. To achieve good game balance, it is better to start small, balance it well and beta test with real players, and only after that implement more skills. That way you can leverage community ideas and needs, plus you'll be able to use real gameplay data to design and balance the new skills.
There will be no support for Lan play initially to cut down the chances of piracy
If players have access to the server code, a knowledgeable hacker will crack the "master server" requirement in under a day, so that's not really a valid reason to not have LAN support.
However there are other very valid reasons to not to support LAN, but they have more to do with ease of implementation and the time it will take.
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As a stylistic note, design documents are typically not written in the future tense, but rather in the present tense. It is just a convention, but there are some clear advantages such as the ones mentioned here:
http://www.ionocom.com/articles/spec. I would add being easier to read to that list.
Also, if you are interested in writing good design docs, this is a good read:
http://www.zenofdesign.com/Writing_Design_Docs_2008.pptSee especially the "no weak language" rule (slides 55-57).
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Some ideas I liked were the learning AI and the co-op campaign. Maybe those could be combined in some way? Like a "community campaign", where the AI bots learn against all players, and are used as opponents in the co-op for some extra challenge.
Could the campaign be expanded to the PvP side as well? Chaining maps somehow based on which team wins, for example. Maybe as a separate game mode?
Also, I was wondering do you really need gold in the concept. Could the gear be bought with ranking points or experience instead to simplify the concept? Or does gold bring something new to the game that couldn't be achieved with these other resource points?