FYI we're not rolling in donation cash; in the past it has covered things like upgrades to the UI library (which we have to pay for), hosting and the domain name, but we haven't personally pocketed any of it yet. It's nice to cover the project's own costs without us having to pay out of our personal pockets, though, and it's still a nice motivational booster when we do see a donation.
If this statement was towards me, then I should say that it never crossed my mind the chance that you're rolling in donation cash. The principle of a chipin model is to promote incentive of what is lacking to a donation model. In other words, kinda like "Hey I get this really good idea that you might be interested, care to help? But if you don't, it may never be completed." when donations feel like "The project is doing fine but if you spare a change or two it might get better.".
ChipIn probably won't be necessary for the near future - we need to finish the 1.0 Windows branch before we think about any other porting. It's an interesting idea but I think it would have to be dealt with extremely carefully. If done wrong, we could end up looking like a commercial venture or something just for financial benefit of the developers, rather than a public open project.
Most likely not the near future, after all the project got this far without it. You may know that the open source community is filled with paradigms, I know that some or perhaps many might see a chipin model as some sort of treason to it's principles, the same people that will curse you if you ever decide to close the source for lack of time/money to invest in it. In my mind is like choosing the lesser evil. New ideas never lack criticism and protest, once they are in place the early critics often look back and say "Wow, that actually works!".
Selling extra services, asking for donations, doing merchandise works to some extent with larger projects, but not with smaller and medium projects, especially with those related to gaming. Open source gaming might need a new direction to be viable in the future and I believe a chipin model is a step in that direction.
I also think that this project would have a larger user base if it had a Linux port, seeing as how the open source community tends to lean towards it (Linux) for obvious reasons. I might be so bold to say that what the Linux needs right now is a good toolkit for quality games and this project shows a lot of potential towards being it.
Just consider it, discuss this idea with others, try to filter empty criticism and let the critical thinking take place as it should. A healthy discussion will not harm anyone.