1. It's very difficult/expensive to make custom key caps that mount to Cherry MX stems. By custom key cap, I mean a completely new shape, like this:
http://3.bp.blogspot.com/-g_Bi0FseNUk/VGBKMdshu-I/AAAAAAAAAe...
We actually did come up with a method for doing this with Cherry MX switches, but the cost was prohibitive. I'll add more detail on the campaign page to make this clear.
2. The actuation force of Cherry MX Reds was just a bit too high. We're making a stenotype keyboard, which should have a very light touch. The Cherry MX Red might have been marginally acceptable, but we're much happier with the lower actuation force of our switch.
3. As you pointed out, the availability of Cherry MX Reds isn't great.
4. The price of Cherry MX Reds is much higher.
Regarding the Topre switches, I agree that 30g is almost too low. Also, the mounting post for the Topre switches seemed challenging from the perspective of creating custom key caps, though we didn't actually try.
As for the openness of the project and there being only one manufacturer, is your concern about availability, control of the IP, or something else?