... 2 here,
2 over here,
1 here,
1 here,
a few here, and maybe a few others I've missed

Also what happens with stuff sent to the ML bitcoin address?
We chose not to convert it yet. Rather, whenever we needed something for ML (like some fast card, or some nonfree PDF, or... the M50 I've got recently), we simply reached our pockets, knowing the bitcoin will offset the expense somewhen - when we'll be able to sell it for a good price

It does feel a bit "underground" to me, and I do feel the need for something better. Other developers are probably happy with their jobs, but - as I've explained
back in April - I am (still) looking for better options. If this could gain enough traction to pay a few skilled developers to work on ML for just 1-2 days per week, it might - in my biased opinion - improve the development speed by at least one order of magnitude.
However, if this is going to make the project
more vulnerable (as in, what if Canon won't like us turning the cheap M50 into a powerful cinema camera?), it's probably best to stay small, as a pure hobby project. Some good legal advice might clear these doubts.
Pay-per-feature with all the money going to a single developer - probably not the best idea, if you ask me. Integrating that feature into the codebase, making sure it works smoothly on cameras X, Y and Z, and fails gracefully on all others, adjusting the code for future changes - in short, maintenance - is going to take significant effort, compared to simply getting some feature working on some particular model. Feature development can come with a lot of fun, but... paying some random contributor to do a bit of tweaking to some new camera port, after someone else did over 90% of the hard work? No thanks.
Some food for thought.