I think a more commercial game company couldn't keep true to the spirit of Dwarf Fortress without seriously changing the usual business model to accommodate it. Part of what makes this game so fascinating is that new features and aspects are continually being added in as Toady continues development - not just new areas, gizmos, and critters, like in the expansion packs to the Sims or WoW, but whole new methods of play, like pump systems, economy, metal alloys, relationships, or the Army Arc. Dwarf Fortress is not a complete game, and Toady is constantly adding in newer, deeper, and more nuanced levels of play. For a commercial Dwarf Fortress box to hit the shelves, one of two things would need to happen:
1) The game would need to see a "final" release. There would never afterwards be a major update, barring maybe a few patches to fix bugs. This would either take forever (thats as in: Duke Nukem Forever), or fall a hundred leagues short of the utterly amazing list of goals that Toady's published (a la Fable). I would weep at this because we would never see the shining beacon of awesome the game might have been.
2) A particularly far-sighted and savvy company might keep a design team working on future releases, releasing them as expansion packs and charging a fee for them. This is pretty much what they do for Everquest and the Sims. The problem here is that unlike those two games, DF is procedurally generated. In WoW or the Sims they can easily add a whole bunch of new fixed content (The Dranei, or a new furniture style), and people will snap it right up. DF is almost all random, and *already* allows for that kind of infinite replay. Even new races wouldn't really fit the bill - I believe there's some discussion on the devlist regarding random generation of some species and cultures. Instead, DF grows by adding subsystems replicating some process that Toady wants to simulate. A really creative game company could sustain a profit for a good while selling such fare, but sooner or later, would end up reduced to tweaking such minute things that the expansion packs would no longer be worth $20 to buy. When people stop buying, the company stops supporting. It's just not a sustainable business model for a big company. A popular MMO or other game with fixed content generates nearer to a constant revenue stream, because they never run out of room to grow.
I would also worry about Toady losing creative control. Big companies like to own the rights, and they have lots more lawyers to worry about the whys and hows of a contract than a lone programmer who works from home and lives on donations. Once the Company, let's say EA, owned the rights, I could easily see all kinds of shenanigans going on in the name of marketing: For one, the whole combat module getting ripped out and replaced with a bloodless Hit Point system - something less gory and more palatable to oversensitive soccer moms, JRPGers, and the ESRB.
That said, going mainstream would have advantages. Toady could step back and get some peons to do the more plebeian bits of coding and bug-fixes while he worked on new features. We would certainly see a team working on the stuff he doesn't really have time for, like a comprehensive help file and a smoother, prettier interface - smarter-than-the-rabble elitism aside, it is a really tough barrier for new players to leap. And say what you like about "OMG, ShINy GRFiX!", some of the stuff that gets posted here looks damned cool in the visualizer, and that's a 3rd-party hack (although a very good one!) that doesn't even recognize all the features.
Probably my ideal scenario would be DF bringing in enough donations for Toady to bring in an assistant or two to handle the more mundane coding and prettify and enslicken the game. However, working with more than one coder complicates the programming (After all, your two bits of code have to work together!) and means modularity, meetings, documentation, and deadlines, so even this isn't really a perfect situation.
EDIT: Some bad grammar annoyed me.
[ April 16, 2008: Message edited by: bigmcstrongmuscle ]