To answer the first question: What is the point/purpose of this? We honestly will not LITERALLY (as in not theoretically) know until Kishi ties it all together, and by all I mean what you pointed out (which +rep to you, very nice digging) along with:
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Obviously: 1 - Madara knowing Nagato and Nagato obviously planning to use the resurrect tech on both Tobi and/or Madara? (Madara obviously did not think he was revived by IWR/Edo-Tensei as we see on the bottom).
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2 - How they all freaking know each other though "supposedly" being from different time-lines, etc...
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As for the syncing part I will get to that below but for most of the rest of your theory/post, I don't think Tobi planned on this happening. Obviously this is a Man/Person/Thing who shows little emotion but the 2-3 times he did was when he was shocked and things did not go as he planned such as Kabuto failing and him losing all of his Paths/Jinchuuriki's which in turn forced him to turn to what he had left AKA Gedo. (I don't think I need to link to pages for this part of my post
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Logically speaking and as FAR AS WE KNOW, Tobi most likely does not want to sync to the Gedo for 2 reasons. 1 - This is easy, just look at an image of Nagato. Plus I don't think he has the power and/or even ability to do so. And 2 - would be that as we learned in this most recent chapter, he released the Jubi/10-Tails at whatever % someone wants to use, but we know it isn't 100% but Tobi and even the Kyuubi still know it's enough to kill anything and everything. So in reality though the Tobi is a master manipulator/strategist/planner, he couldn't and/or didn't account for these things happening but still knows what he has in the Gedo at 75% (give or take) is 1000% better than anything + everything + whatever else you want to throw into the equation. Going this route will obviously allow Tobi to "complete" himself and maybe give him the power to sync or force/make Sasuke sync, etc...
There is a 3rd semi-logical option and that would be a mixture of 1 and 2 along with the fact that maybe if Tobi syncs with it he can't use it as a summon which as we know is needed. This can also be proven/shown by Nagato AS FAR AS WE KNOW not being able to summon Gedo, though being able to use it's other features b/c he was synced to it, as opposed to Tobi who can summon what even before it became the 10-Tails was one of the strongest creatures/things in the Narutoverse. (Think about it: Why wouldn't Nagato have just used it as a summon instead of some puny bird, crab and dog that replicates? Gedo as just a summon would have wiped out Konoha and Nagato/Pain wouldn't have to have even used ONE shinra tensei.)
I would think at this point, since Akatsuki is no longer really in existence (remember how many days, chakra/energy and such it took from about 10 of the strongest rogue and/or enemy shinobi around to seal one of the tailed beasts?) there is no syncing BUT as far as sealing the Gedo in let's say...SASUKE who then becomes its Jinchuuriki and casts the Infinite Tsukuyomi? I mean remember how much stress it caused on Itachi and how weak he was after using it on Kakashi? To have it going on 24/7/365 while Tobi is controlling the everything, everyone and the world and Sasuke is doing all the work? I don't want to do that much digging to find the chapter but remember Tsukuyomi needs to be awakened and though we haven't (at least I don't remember this happening) seen Sasuke use it, he does use Susanoo which can only be used after awakening Tsukuyomi and Ameterasu, so we can logically say with certainty that Sasuke has awakened Tsukuyomi. Plus I know as of right now Tobi has said he plans on becoming the Jibu's Jinchuuriki but remember he still has Madara to deal with and he is aware of that, AS WELL AS being able to manipulate Sasuke at will so he could potentially seal the Jibu in Sasuke and let Sasuke/Jibu fight Madara, Naruto/Kyuubi, etc...
As for the final battle/ending...well this is the only part I do disagree with you on. Since even Kurama/Kyuubi/9-Tails has come out and said that the Jibu at 1% (exaggeration but you get my point) could wipe them all out, I would have to think (and agree with you) Tobi loses control at some point that they ALL have to fight against this thing. (I would write a longer paragraph but I am too tired). Also not for nothing...I do think Kakashi, since he was really the first one to realize what was going on as well really grasp the situation... and by the way Kishi writes with his hints/foreshadowing, etc... I feel like what Kakashi wanted to "try" was his Master's tech: DDCS (Dead Demon Consuming Seal). So for the immediate future leading to the ending I would like to predict Kakashi, following in his father's footsteps, saves his comrades (kind of like how he died the first time) or at least helps/aids them in a BIG way by taking what power he can from the Jibu with him (Like Minato did to the Kyuubi). Remember Kakashi put it all together and it explained it to everyone in the chapter (obviously with help from Kyuubi) but I think he feels and/or knows that if he can (with the help of Kishi's legendary Plot no Jutsu) somehow seal the little chakra/power the Jibu has from the 8 and 9-Tails. Call me crazy, I just feel that Kishi loves catching people off guard as well as pulling you know what out of you know where (as you beautifully put it: "Unless of course, Kishi ***pulls") would be a perfect way for Kakashi who has "lived his life in regret" to meet his maker.
