I think I misunderstood you. I was not talking about using parts of SC to implement in Renoise’s own sampler, but offering a SC binary (maybe with some additions to better integrate with Renoise) as an individual download to Renoise users. I think neither is actually very realistic, and I rather have them just finish the Renoise sampler and Redux.
Of course integrating GPL source code into Renoise (or any other software) itself would require it to be GPL as well. It could still be commercial and all, not much would really need to change, but often business models seem to depend on the secrecy/exclusivity (rather than on support for instance).