There's two sides to this. One side in my view consists of two aspects: 1. if we somehow pre-fund any projects, we will be have that funding exploited and sub-par work produced. 2. if we fund net-# then we can be rest assured that only quality work will be supported (or no funding will be released).
The other side consists of the fact that we want to get away from the notion that "someone else" should always pay for all development. I have to fund my projects and all my contributions. So do others. Their hours on Github don't get funded. Do we want to say that that time and effort are of lower quality and value than potential future contributions that would "require" funding?
Let me think about my answer here for a bit. I'll put up a post if I can figure something out.