You can definitely clone 5E and ORC is 100% irrelevant to whether you can (if you think it is relevant, you literally don't understand how the law works). That's not even going to be a question. WotC launching a legal attack on someone cloning 5E outside the OGL would be absolute suicide on multiple levels.
The absolute best-case scenario for WotC attacking essentially a "non-OGL 5E clone" is that WotC causes itself massive PR damage, and loses a bunch of copyrights, all in order to damage a company that's not really a competitor, so it essentially gains nothing. But the rest of the industry gains a precedent showing what actually is copyright'd, and how they can work around that, which would be a huge boon.
That's the best-case scenario.
The worst case is the same or even more PR damage, it loses on every single copyright point (which is not that unlikely), and might even end up being forced to pay the costs of its victim. Then the industry learns that it can freely clone 5E without any fear at all, and WotC has essentially thrown away any threat value it had.
As for "they may not be able to revoke the OGL", yeah, maybe not, but they are acting as if they believe they can 100%, and are making all their decisions on that basis, so it's kind of irrelevant. We won't get a better OGL until/unless they stop that.