Thinking of licenses in terms of threats of lawsuits is exactly right.
The purpose of legal counsel before the fact is to be professionally risk averse, and so the only measure of success or failure is gong to be in terms of ability to mitigate risk.
Personally, if I were in Sony's position, I'd do exactly the same thing, especially if my parts supplier were Qualcomm and I was contractually obligated to not reveal the contents of the hypervisor on the Snapdragon ARM processor I used (and in fact could not, because only Qualcomm had it in the first place), or if my supplier were nVidia, and I couldn't reveal the signing keys needed to allow you to comply with the ability to run your own kernel because, frankly, again, only nVidia has them.
Both of these derive from governmental obligations these companies face when these chips are used in mobile phones, and unless those go away, you have a chain of risk that leads to needing to rewrite to get out from under the GPL.
You're wrong
The purpose of legal counsel before the fact is to be professionally risk averse, and so the only measure of success or failure is gong to be in terms of ability to mitigate risk.
Personally, if I were in Sony's position, I'd do exactly the same thing, especially if my parts supplier were Qualcomm and I was contractually obligated to not reveal the contents of the hypervisor on the Snapdragon ARM processor I used (and in fact could not, because only Qualcomm had it in the first place), or if my supplier were nVidia, and I couldn't reveal the signing keys needed to allow you to comply with the ability to run your own kernel because, frankly, again, only nVidia has them.
Both of these derive from governmental obligations these companies face when these chips are used in mobile phones, and unless those go away, you have a chain of risk that leads to needing to rewrite to get out from under the GPL.