I love the idea of tying the canons together (though I'd prefer they didn't), but man... Every time I see the words "time machine" thrown in, it always sounds so silly. And this is really a bummer for me, because I really like time travel plots (Legacy of Kain, for example).
Unless the plot initially involved time travel, it's very hard to actually make it sensible, and just... not silly.
Well, I will hypothesize.
Imagine that at the end of Lords of Shadow 2, Gabriel the Dracul becomes an even greater evil than Satan, threatening destroy the world effectivelly. Then a time traveller or some other sort of time manipulator (Hell, this could be Trevucard himself, wanting to give his father and himself a new destiny after happening upon Frankenstein's hidden Time Machine!) is sent back in time to prevent that Gabriel is ever abandoned as a bastard from the Cronqvist family, in hopes to avert his whole destiny (and even Zobek's own plans). By not being abandoned, Gabriel Cronqvist does not become Dracul, but his son in this new timeline, Mathias, becomes Dracula.
I do not know how the rest would unfold, however. I think that for a time-travel plot tieing to the canon to really work, the time-traveller/manipulator would have to go even farther and prevent that the Brotherhood is even formed, maybe by killing Zobek while he is wearing the Death Mask (Which would effectivelly make him the final boss, and defeating him would make the Death Mask give rise to his soul becoming the canon Death, whose purpose is to serve the Dark Lord, also justifying Death's apparent hatred for time travellers), so the Lords of Shadow are never even born, as they are the whole reason as to why Gabriel/Dracul even exists.
If this happened and the Dark Lord Carmilla never existed, then the Bernhardts would not be driven out of their castle by her, leading to Walter becoming the Dark Lord and kidnapping Rinaldo's daughter, sending him in his quest to defeat Walter (LoS make it clear that this same thing happened in it's timeline, around Gabriel's time). An older Gabriel would give birth to Mathias Cronqvist in time for him to become a Knight (Remember the dates. Lords of Shadow is 1047, and Lament of Innocence is 1096. The dates do match) and Rinaldo to be stranded in the forest for a long period, and then the rest would unfold as it did.
Let's not forget that, somewhere inside Berhardt Castle, there IS a time machine constructed by Frankenstein, that was mentioned since the very beginning. If they decided to use it, they'd not be pulling it out of their asses to make it work.
I'm starting to think too much here xD