I have not read through this entire thread, so if I'm being repetitive, please find it in your hearts to forgive.
I used to be where Sean Malstrom is now, back when I first discovered DF. "ToadyOne is keeping this glorious thing from achieving its full potential! How horrid!"
While Sean's solution is commercialization, mine was open sourcing. I pressured Toady quite a bit, back then, to open source at least part of his code. He had many excellent reasons why he wouldn't - his control of the game, the quality of his code, code bloats, forks. I understand that these days, there's a Linux version and a few open-sourced front-ends. But the core DF remains closed-sourced as well as non-commercial.
What I have come to realize - and which I think Sean is has not realized, thus his hangup - is that DF is more than a game product, it is a product reflective of its creator's and players' obsessions. To remove that obsessive quality, either by ToadyOne relinquishing control in favour of a larger development team, faster iterations, and (perhaps) more sound software design and process, or by catering the game to a larger cadre of players with a an average smaller degree of OCD required to play the game in its current state, would be to water down that product. The product stands on its own not necessarily only as a game, but as Toady has described it before, a "fantasy world simulator". That sets it apart from toys to be bought and played with for a while, towards something with lasting appeal and inherent value. Compare "Ticket to Ride", a board game with a train theme, to constructing your own vast and complex model railroad. You can play with the railroad, but its value is not necessarily related directly to how well it plays, nor how many people play with it.
Imagine if a company - even a well-intended, smaller outfit - bought Dwarf Fortress' code base and name, hired ToadyOne as lead developer, and commercialized (or open sourced!) the game. The feature request list would now be driven by what marketing saw the player base - or potential player base - as wanting. Chances are that pretty graphics and streamlined interface would be first on the list. Second, probably armies and conquest style gameplay. These features or others would be implemented on a tighter schedule, and would be created by a team of coders, so the existing code would probably need to be cleaned up some. This would lead to finding potential speed improvements, if only one or two hardcore simulation algorithms could be streamlined and "faked". This would facilitate gameplay and reduce long-term simulation speed issues - great! But the underlying simulation would be weaker. This would produce fewer emergent side-effects, i.e. less "fun". The masses would be placated, money would roll in, new fans would be gained - but the obsessiveness that is the game's hallmark is lessened. The 20 year timeline to 1.0 would be replaced with a 2-3 year timeline. New features would not be implemented with the same degree of attention to detail and would feel weaker and bolted-on, compared to the core content developed over the last better part of a decade. Most importantly, the quality of DF as a "fantasy world simulator" would be lost in favour of a playable game sooner.
That's a best-case scenario - a worst-case scenario would mean a from-scratch, shallow total rewrite with lots of associated marketing and a $50 price tag. Tons of buyers, lots of sales and $$$, but the game would be popular for 2-3 years and then relegated to a bargain bin while the dev team worked on a new version with a new code base ("Slaves of Activision: Dwarf Fortress II the MMORPG").
The multi-billion-dollar game industry depends on continuous reinventions of the wheel, repackaged for an additional $50, and released on a cycle. The last thing the game industry wants is a "fantasy world simulator" that stands the test of time for decades at a time, and which eats 1000+s of hours of continually fresh gameplay for the same price as a 6-hour long, scripted, linear game. It doesn't matter how pure the ideals of the company - there is no way that DF could continue to achieve its full potential if it was commercialized, nor if it was open-sourced with the intent of bringing it to the masses. While Sean takes the quote about "society" out of context in the blog post, DF has the potential it does in large part because it is produced entirely outside of the scope of a market-driven or even "social" economy, as an obsessive project by a single individual dedicating his entire life to something larger than himself.
Having said all that, I hope we will continue to see "Dwarf Fortress knock-offs", both commercial and open-source. They won't draw away from and compromise DF's fantasy world simulator goals, but they will produce playable instances of sub-sets of its features, and may even add some ideas of their own. It sounds like Tarn's donation model, in light of his frugal lifestyle, is working great to fund its development at present, and I hope it continues to be able to do so such that a more commercially viable model won't be required.
Tarn, kudos to you for your honesty and willingness to make this your life's work in the face of easier options. Don't listen to misguided people (like me four years ago) who are trying to complicate your project by bringing business acumen and user feedback and process improvement and whatever into it. Do what you do best and stick to your guns - you know what's best for you and Dwarf Fortress, other people just think they know what would be best for them if they were you.