I disagree with Kahil strongly. "There is no market for mass plugin production." Depends on 'mass' -- if the few hundred users a year who download my plugins would become paid users, that's pretty good. The 'market' is there in terms of size (hundred-plus is a good start, thousands is better).
"it makes no logical nor financial sense to start making plugins for profit." Well, not if your belief is that you can buy commercial plugins and then go give them away, no. And possibly from the other direction: it's not necessarily feasible, even if people like you didn't think it was your right to undermine commercial-thinking developers, people like me living in high cost-of-living areas of the US (let alone the world!) have a hard time making ends meet at $5-10 a pop. At least, not until I hit a few thousand paying users, then we'll talk! ;)
Now, you also basically make statements that it isn't feasible because you could just give it away. That's not quite true.
If you agree to the terms of the purchase of a commercial plugin, you are bound by those terms. Not all WP plugins are GPL, and they don't become GPL just because you say so, so redistributing a non-GPL (or other non-free license) plugin for free, modified or not, would be a violation of that license/purchase, and a violation of the law. Could you do it if you wanted to? Yes. Should you? No. Is it any different from software piracy for you to redistribute a plugin that you purchased as a commercial product? Nope, sorry.
Should we get into an argument over whether or not plugins can be non-GPL? No, as it's been discussed and debated at length, and there really isn't clarity in the GPL on this subject. And this isn't a discussion of GPL -- it's a discussion of whether you would pay for a plugin. And I >think< you have actually answered you WOULD, if it were a custom piece, or otherwise unique (tell me if I'm wrong on that, not trying to misrepresent you).
Of course, if it's unique, but interesting to more than just you, regardless of whether it is GPL, you don't HAVE to give it away for free. You see, that's a CHOICE when purchasing something that was GPL based. You can ask for the code, you can distribute it for free, but it isn't required of you -- you CAN let someone make a living off of GPL-derived work, or off GPL-related work.
We can agree to disagree. I think the reason it's not financially feasible is because of the exact mindset of folks here who say they'd never pay for a plugin, but might on a rare occasion donate.
If you would donate to EVERY author whose software you use, plugins or otherwise, you are helping maintain the OSS world. There is no such thing as a free lunch. Automattic wouldn't be a 'business' right now if it wasn't for WP, and WP has developed over the past few years because of many people outside the core team, who gave time for free. In a sense, much OSS has become like shareware of old, too much sharing, not much paying (or, not much feeling on the part of the users that they should pay, that there's a reason to, a benefit to... that by not paying/donating, they are actualy 'harming' the 'ecosystem'.
So, I agree with you questioning financial feasibility ON THAT GROUNDS, that anyone who feels that they love WP, love the plugins they use, but wouldn't pay a cent, because after all "it's free software", don't feel there's a 'need' to financially support such developers. Thus, self-fulfilling prophecy. ;)
To the best of my knowledge, Automattic has salaried employees. I'd bet there's a lot of WP development at this point whose 'cost' is being paid for, is being underwritten in many ways, some direct (support for some big installations of WP-MU or something), some indirect (I don't know for a fact, but I'd hazard a guess there are indirect sources of cash there).
Contrast that with much of the 'secondary market' of themes and plugins goes greatly unsupported, with donations and purchases too few and far between. One or two in the plugin side of things has broken out and developed and sold suites of plugins with paid support and help. I'm likely going to HAVE to follow that model in the year to come -- I have no choice, with users not donating enough, but the support emails come and go. (Joni, thanks to you for being a supporter both in words, and in donations!)
So, I'd agree that there are issues with making money in OSS, but the issues are of education and self-responsibility in the era of OSS. If the software is good and useful, pay for it -- or, if you can contribute back (forums, support, coding, etc.), give back in 'bartering' methods.
Just because it's "free software" doesn't mean someone isn't paying the bills. In my case, I underwrite most of what I do with my day job. In the case of WP core, I'd presume by now much of it could be underwritten by Automattic. Heck, most important Linux development these days are full-time-employed people at major companies, either the Linux resellers (redhat, et al), or custom software or hardware developers (who contribute free drivers, free enhancements, but because they are leveraging the 'free' software in other ways... Go look at the TomTom GPS free downloadable bits, for instance...).
<off the soapbox>
(and the odds are I'm so busy with the job that DOES pay my bills for the next week that I won't be reading this potential-for-a-flamewar actively... anyone can feel free to write me offline in support, or disagreement! ;) )