This topic has come up pertaining to Farm Hack several times, and is worth exploring further. It would be a great project for a localized farm hack crew to take on in their area. There are a few examples of farmer groups who have done this.
Concept: Sharing of tools and machines allows greater and more affordable access to machines and tools for farmers to increase their efficiency and production potential. This structure could also be used for educational and design processes - members of the collaborative could work to improve their tools/machines and develop new ones, as needs arise.
Known examples: Intervale farmer cooperative in VT (not many details available online) http://intervalecommunityfarm.com/resources/ Sustainable Agriculture Tool Lending Library in NC: Ben write a blog post on this topic last year: http://www.youngfarmers.org/farm-hack/2011/04/12/farmhack-sustainable-agriculture-tool-lending-library/ - this group received a grant to start the library
Resources: University of Wisconsin Center for Cooperatives Report - http://counties.cce.cornell.edu/washington/Ag/FieldCrops/Outsourcing/44MachCoop.htm