I´d guess a scheme alike Guardian/GPro with having free version/
server version is not feasable, cause by giving your algos out the
whole project is matter of time till one talent cracks it it and maybe
even offer reverse engeneer service from it.
Anyway, i think a free version and a pro version might be nice catch.
Pay per project?
One time fee for unlimited projects and patches?
Yearly rate for unlimited projects and all updates/upgrades?
In my opinion you may can measure $ on the take up of G/GPro