There's a little bootstrapping problem there: often you need a RepRap in order to develop on one. But aside from that the idea is reasonable.
The Open Source Ecology guys have a good system of getting pledges and donations in.
[
openfarmtech.org]
Kickstarter seems to work well, at least it did for Makerbeam:
[
www.kickstarter.com]
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What are the development pathways you want to heat up a bit?