A Church Planting Model for Agencies/Institutions

The BGAV has a long history of planting churches. We identify locations for new churches, we send people to be on the launch team, we assess and recruit church planters and provide funds to get the new church going. The funds help with two parts of the startup costs. Our New Church Investment Grants provide funds for things a new church needs (equipment, marketing material, curriculum, etc). The salary assistance funds help pay a portion of the church planter’s salary for up to three years.
We fund new churches this way because we believe that after three years they should have attracted enough people to support their work. Another way to say that is if you can’t excite enough people in three years to be self sustaining then you probably aren’t going to make it long term. Of course if the new church multiplies into another site or plants another church then they can once again access BGAV funds for church planting. I think this is a reasonable and right way to do church planting and it has served us well.
What puzzles me is why we don’t do the same thing with institutions and agencies. We provide BGAV funds and people to help get the new initiative going and then have the expectation that after a period of time you can be self sustaining. All of our institutions/agencies have other funding sources besides the BGAV for their budgets (with the exception of WMUV who has a unique relationship with the BGAV). At what point should we expect them to be self sustaining?
Perhaps the timeline to self sustaining should be longer than three years. For the sake of discussion let’s make it ten years of BGAV support to get you going. After that ten years the institution/agency would be welcome to come to the BGAV to request funding for new initiatives. But after ten years if you can’t make it on your own, then you probably never will.
There is also an expectation of our church plants that they contribute to the BGAV. We expect that contribution to be in the form of dollars not just relationship. We expect our church plants to help “pay it forward” and help us launch additional churches. What would that look like for our institutions and agencies to pay it forward to fund a new generation of mission partners to the BGAV?
If we expect a church to be self supporting after three years then is it so unreasonable to expect our institutions and agencies to be self supporting after 10, 20 or 120 years?