Recently I was thinking about possibilities for funding the open source project. An approach that I came up with could be an addition to the standard funding models is lets call it a delayware. I did a quick search on google to see if somebody has already thought of that, and that does not seem to be the case (or I am using the wrong keywords to search)
The essense of the idea is following:
1) Paying customers get the newest version of the product
2) Non-paying or non-contributing customers get the previous version of the product.