I came across some thread in the add-on section ( [Paid Work] Photo Contest Script )where a few people seemed to have gotten together to pay a share for an add-on. It also seems as if that effort then fizzled though that may not necessarily be true.
Few admins are willing and able to just go out and commission a coder to create an add-on considering that many add-ons require considerable effort (billable time, if you will). Many admins are willing to financially contribute to the development of an add-on that they need. The Photo Contest Script clearly demonstrates that there are some ownership issues though.
While one can imagine all kinds of elaborate schemes to compensate the coder and the fractal owners none of those schemes are particularly practical from an implementation and administration point of view.
Then there are trust and follow-through questions. Taking the Photo Contest Script as an example, many have pledged support but it appears as if no actual transactions took place yet. It seems what's needed is some sort of escrow service which holds the payments from the pledges and disburses the funds to the coder. That way the coder is sure that he or she will get paid, and the admins are sure that there is actually code being developed before their money gets paid out.
The ownership of the script remains one of the sticky points of the whole scheme though. Some admins may be fine with releasing the script into the wild after it has been created, others may want to get a return on their "investment". Issues of long term support for the script are also to be considered.
While I don't have the time to do this myself I am wondering whether there's a market for a commercial script depository? That company would hire coders to create add-ons. Admins would be able to invest in add-on creation (so that coders can get paid) and the company would then sell the add-ons for eternity to come. The coders and the investors would receive royalties on add-on sales and the company would collect overhead on development and transactions to stay financially viable.
The true difficulty I see is the global nature of the industry. I wouldn't trust a non-US incorporated company and likewise I'd expect that the Euros wouldn't want a US based business to run the show. I am conveniently ignoring the rest of the World and issues they would have with either location.
Ignoring everything I just wrote the only other solution seems to be that a bunch of people pay for an add-on, and then it's released as public domain and that's the end of it. Users can then pay the coder for support.