All right, so with only another probable 2 chapters left and the first to be released in a matter of 7 days, I think it's time to theorize how it will all end.
Personally (because I love paradox theories) I think that the past incarnation of Jack can see Oswald, Alice and Cheshire, and that this is the entire reason why Jun has never shown us Jack and Oswald's final confrontation where Oswald is dismembered. I think that rather than Jack being the one to have dismembered Oswald, it was Oz himself in his present incarnation - as this would also explain why Jack didn't remember having murderd Oswald himself. This could very well be a part of Oz's deal with Jack for all we know.
I'm still going to state that I also believe that Oz is Lacie's Chain. I don't know what it is, but I just feel as though Jun didn't make Lacie's Chain in that form for no particular reason, and while I'm not able to discern how the theory would fit, anything really is possible in a fictional universe.
I also believe that Ada's interactions with the past incarnation of Vincent was the entire motivation for Vincent's idea of using Ada in order to get to Oscar and obtain the Vessalius Key. To me everything that's playing out now has already happened and the timeline as it exists is in a state of constant rotation without an end or real beginning because of the paradoxes imposed.
As a final marker to my theories, I'd like to talk about Dug's Chain. I feel as though it may or may not get brought out in Retrace XCIX, as Dug's Chain likely isn't very combatant (like Tove) which is why its never made an appearance. Additionally, I believe Dug's Chain's likely going to coencide with the Jabberwocky poem from Through The Looking Glass and What Alice Found There, as it would suit the present Baskerville theme. There's already a Jabberwock, Jub Jub Bird, Bandersnatch and Tove among the Baskervilles, so it'd be fitting if Dug had either the Borogove or the Rath.
Finally, there's the depressing theory that all of Pandora Hearts may just be a dream in order to fit in with Alice in Wonderland - and the series would conclude with Oz reawaking after falling into Lacie's Tomb, with the Coming of Age Ceremony following naturally as it was originally meant to. I don't like the theory, but it unfortunately seems the most likely to me :/
Anyway, that's all I really have to say, leave comments and opinions below if you want... we're almost at the end and I'm so conflicted by excitement and depression it's not even funny :p