If a *proper* sixth game that concluded the story were to be made, how would it avoid scaring off new players with it's complex plot?
Forgive my naive optimism. I know things are looking grim, but we didn't think we'd be getting such high quality remasters, especially one that practically redeemed Defiance as a title, and it's pretty apparent that Ascendance was made as a budget game than a proper "continuation." Perhaps the coin will land on it's side again. You never know. At the very least there's no harm in pretending.
In short: LOK has a very complicated story, and if a sixth game that took place after Defiance (and was NOT made by Bit Bot) were to be made, it would have a hard time attracting new players due to the large amount of plot threads that players would have to wrangle through just to understand what was going on. Either they'd have to play 5 other games (at least 3 if we skip both Blood Omens, which sadly don't have remasters yet) to understand what's going on...or they'd have to just jump in blind and hope to understand all of this craziness about vampires, time travel, and Elder Gods on their own.
To fans this would be no issue, but newbies? Utter confusion. I suspect this is part of why we don't have a proper sixth game. That investors see such a deep narrative and think the average gamer isn't going to be able to play more than a few minutes because it's "too confusing" for them, so they reject it on principle.
I don't agree with that thinking, but it does bring up a good point. How would a sixth game be able to attract new players who weren't able (or interested) in playing all 5 other games to understand the plot? In an ideal world, it would just exist and be targeted for a small audience, but sadly the gaming industry doesn't work that way. Sure, the remasters have gone a long way towards making the originals more accessible, but a lot of people are sadly pretty resistant to playing older games today and even those who aren't, again, might not wanna play 5 games just to understand 1.
My suggestion would be to do what the new GOWs did, and have a story that's both self-contained but also serves as a coda to the arc established in previous games. The Dark Prophecy was going to be about the present day Kain time traveling back to meet his younger self, so why not do something with that? Perhaps start the game off as an interprequel between SR1 and BO2 about a younger Kain gaining power through deeds that lead to his rule becoming what we see in Soul Reaver (perhaps we even get to see a newly resurrected Raziel?). Then halfway through, the Kain from Defiance suddenly shows up and the latter half of the game turns into a tragic extended finale where the younger Kain witnesses what he's fated to become, while the modern Kain (who'd be the main PC of the later half, sorta like RDR2) accepts his ultimate fate, whatever it may be. The goal would be to give the original saga a proper ending, while leaving room for more interprequels set in the long period between the games following the younger Kain (or even other characters).
Or maybe it won't happen at all. Maybe not. Maybe so.