If the code is available in a form that enables people to build it, that seems likely to reduce sales considerably whatever the licence. (In any case, I don't think CC-ness of the licence is the relevant feature.)
If the source code is available then nagging, begging and crippling are easily removed. (Unless the crippling is a matter of omission and the uncrippling bits are paid for -- but that's just one variety of freemium.)
Your first suggestion, a good plugin API, seems like the way to go. moridinamael, what advantages do you see to open source over a plugin API?
Other possible options:
With respect to making the source available, the consequences depend on the target market and the price. For a multi-thousand-dollar product aimed at STEM professionals, yeah, people will bother to recompile without the offending bits. For a mass-market app priced at $0.99 no one will bother.
But I agree that some plugin API looks like the most natural way to proceed.
If it's worth saying, but not worth its own post, then it goes here.
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