Besides the fact that existing systems work fine for this, the idea that users pay for a fix or feature is ludicrious.
Users are terrible project managers. They report things as bugs that aren't bugs, they request features that don't improve the product, they in general have a low hitrate in terms of providing successful direction for a project.
Setting up a system where users pay for a _specific_ thing to happen is just asking for trouble.
Users paying for development they already find useful, or for concepts that they believe have promise - that's the way to do it.
Yeah, that's all true, that users sometimes think of something as useful and it is not. Nothing to be done about it, except education. But let's say some users want of an open source program to integrate some graphs somewhere. They go to a social media and they ask the users. "How many find useful these graphs?" The users hit like to the feature, and they immediately transfer a small value to the owners of the project. In case the sum of all the values of all the users is enough, the owners of the project may go forward, accept the funds and allocate resources to implement this feature.
Users are terrible project managers. They report things as bugs that aren't bugs, they request features that don't improve the product, they in general have a low hitrate in terms of providing successful direction for a project.
Setting up a system where users pay for a _specific_ thing to happen is just asking for trouble.
Users paying for development they already find useful, or for concepts that they believe have promise - that's the way to do it.