Observation 1) Has anyone else noticed that Father's robes alway seem to be crossed right over left? Or involve a strip of cloth crossed right over left across his chest? This means little or nothing to Western audiences, but if you wear your kimono that way in Japan, you're indicating that you're dead... (I got giggled at once, three or four years ago, for doing that before I knew any better.)
Observation 2) Sloth was last seen in some kind of a cave. He seems to have spent most of the manga, if not all, in that cave. Hohenheim is currently on his way to some kind of a cave ("the inside of (a) mountain"). Coincidence?
Observation 3) So, Elric is Trisha's maiden name, and Ed and Al are bastards. I wonder if this affected their childhood at all, regarding how they were treated by their peers and fellow townspeople. This insight also lends a whole new level of irony to the popular Englishism of Ed calling Roy "Colonel Bastard". Does this make Ed "Major Bastard"?
Observation 4) It appears that the manga method of making a homunculus has finally been fully spelled out. Take one living human, add essence of Kenja no Ishi, allow to frappe on high till blended smoothly. Drink chilled?
Observation 5) Knowing this, and knowing also that apparently homunculi are sterile, fatheroftwo!Hohenheim is almost certainly not a homunculus as we are familiar with them. He's also obviously not human, both from his uncanny healing abilities and his inability to age. One would presume, therefore, that he is some kind of alchemical construct other than a conventional homunculus, possessed of their healing abilities and agelessness, but made in another way (probably experimental, from Father's curious surprise about his current condition and whereabouts and ability to reproduce). Also, he seems to have either run away or been thrown away, but not before learning enough about Father's plans to be warning Pinako to get out of the country.
Observation 6) I suspect, personally, that Hohenheim is a human-like being made entirely from alchemical scratch with raw materials--in other words, the complete and correctly constructed form of the sort of being that Ed and Al produced, in their attempt to create Trisha a new body. I also suspect that the array Ed found was among Hohenheim's papers precisely because it was the array used to create him.
Observation 7) May I suggest my friend kawree's "Greedling" as a title for our exuberantly cheerful new friend? It's got a great double meaning, both as a combination of "Greed" and "Ling", and as another way of saying "little Greed" or "Greed Jr."...
Observation 8) Unlike most of the fan speculation I saw out there pre-54, such as whether Roy would finally get ganked, and whether Scar and Mei would meet Al and Ed and Ling, and who Father and Pride and Hoho are...my biggest personal question was, "Will having eaten Ed's BOOT prove to be a plot point later down the line?" I continue to wonder. I humbly note that Father did not, during all that Look-At-My-New-Toy! poking and prodding, appear to give Ed any preemptive treatment for indigestion. He also neglected to make Ed a new boot, but given that Father's is apparently just as creepy when he's being helpful as when he's being scary, perhaps that's just as well. Likewise, are homunculi (other than Gluttony, of course) susceptible to such things, and if so, will our new little Greedling be shortly receiving a rude reminder of the drawbacks of having a body?
That's...pretty much it for now, other than all the other observations and questions others have already voiced ad nauseum.