>An alternative take, which I'm sure won't be popular, is that now, with an interpretation taken to the extreme, a megаcorporation can basically steal your (let's say a small startup's) platform (in case you refuse to sell it for ethical or some other reasons), by re-implementing it and investing much more resources which you don't have, to make it more attractive to customers.
GNU/Linux, a free reimplementation of AT&T's Unix interfaces, is largely why commercial Unix isn't really a thing any more.
Yes, but the situation is a bit different -- the majority of UNIX rights owners were actually promoting open standards through initiatives like POSIX, X/Open, so the re-implementation did not violate the copyright. As far as I know SCO's suits were not about interfaces of any kind, and the Linux kernel uses C standard library and other posix compliant libraries as an interface.
GNU/Linux, a free reimplementation of AT&T's Unix interfaces, is largely why commercial Unix isn't really a thing any more.