I think what I might do when the time comes is to just open up a contribution thing at my site where contributing different amounts will entitle you to different things, such as:
Option A -- A copy of the initial module (basically a "pre-order", if you will)
Option B -- A + entry into Beta testing
Option C -- A and B + entry into Alpha testing
Option D -- A, B and C as well as any future module releases
Updates for bug fixes and such will always be free, as will periodic ship and component additions.
Maybe I'll just put a donate button on there and allow anyone who donates over a certain amount to help test and offer the initial module for free to everyone to get it started. I don't know--there's still a lot of time until I really need to start thinking seriously about it.
I do appreciate the sentiment though