Let's be honest, a hefty portion of players won't be shocked at the comment made at the end of the trailer. There is also huge room for this to be Solus blowing smoke. After all, spreading chaos is his thang, and what better way to get some in-fighting or debating going than to have the WoL and co. doubting Hyde (or our connection to her).

Given we are still completely devoid of anything from Big Daddy Shadow himself, we cannot possibly come to any conclusion about whether he/it is evil, much less whether he/they are ancient-primals until we get our teeth into Shadowbringers. All I WILL guess is that there will eventually be some revelation about how it's not so much about one or the other being evil, but more a case of how good/evil one is from the other perspective. At the moment, Ascians consider Hyde evil for reasons, and all we have to go on regarding Zodiark is the hints and comments that he's the big darkness and eats worlds and that's bad... But we can see Light doing the exact same thing, just inversed.

TLDR; wait and see.