I'm confused are you saying you want Hydaelyn to be evil and we kill her or...? I guess it would be a weird twist if Hydaelyn is evil since there has been very little set-up for it. Somewhat greyer then we thought? Maybe. But evil? No.
I'm saying that it happening is very likely. There's so much buildup to it right now in Shadowbringers that it is not out of the realm of possibility. We know Hydaelyn is incredibly terrifying and so is Zodiark. If we got a plot that we kill both gods I think it would be epic personally. Sure, we've been with Hydaelyn all this time and we think she's mostly helping us but personally I don't believe she is. WoL is incredibly terrifying and death itself like Elidibus said. All I'm saying is that if you guys aren't ready for the Hydaelyn is evil trope coming down the line then you're going to be really disappointed.