I'm not knocking the effort it takes to clone its GUI, plugin API (OpenFX [0]), or basic plugins. But I'll also point out as an alternative that The Foundry offers a free non-commercial version of Nuke [1].
It is the same as everywhere else - honest users are seriously harmed by licensing policies while thieves are just using the latest torrent release.
Nuke is, no question, an industry leader, but an open source competitor will hopefully make the featureset of this kind of software more widely available also for projects with very low budget [while starting]. Meanwhile TheFoundry management should look at Unreal for licensing ideas.
Qt has a somewhat similar provision in their licenses [1]. Personally I think it's acceptable, but walking a fine line. It's an attempt to make sure users can't skirt paying for a commercial license if they are, indeed, commercial.
I would hope that if you contacted their customer support and politely explain how your project was using the free license in the spirit it was intended to be used, they would allow imports from the free version, say as a once-off when you purchase the licenses.
Natron is a node-based compositor, there have been many over the last few decades.
Another open source node-based compositor is Blender which also has an non-linear editor.
Lots of compositor customers just buy Nuke, Fusion, AE, etc to process sequences through different commercial plugins; having an open source wrapper to run and control the plugins is an excellent alternative.