Besides the actual mystery of Clara's identity - so far I think we have two open questions (which we can add to as the episodes progress): 1) Who was the woman in the Newsagents who gave the Doctor's number to Clara? 2) Does the Great Intelligence have a master-plan and if so what is it?
I haven't a clue to #2, but for #1, we have some suspects: Sally Sparrow -- She was the first person I considered while watching that scene. But I don't think she actually has the number. Also, Carry Mulligan has a bigger career now, and therefore isn't -- so I'm told -- likely to return to Doctor Who. River Song -- She has the Doctor's number, and the character is known to return this season. But please ... don't be River. She's worn out her welcome like the Mississippi during the rainy season. Yeah, that's a placeholder until I can think of a more clever line. Martha Jones -- She has the Doctor's number, and she's used it to summon him. Freema Agyeman isn't noted to return this season, though. Donna Noble -- Didn't she call the Doctor in the episode "Midnight"? Even if she didn't, she's likely to have his number. She just doesn't remember it. Or Who it's for. Or even why she'd call it. Never mind, she probably already cleared that number from her contacts to make room for all her other gossipy girlfriends. Rose Tyler -- Isn't she off in another universe? Although it looks like she's returning. I think. Amy Pond -- Did she leave her cellphone in the TARDIS, or did she have it with her when she got touched by an angel? And Rory probably still had his. Remember the end of "A Piece of the Action"? Now apply that to the 1930s and Earth. And Doctor Who instead of Star Trek. Someone in U.N.I.T. -- Brigadier Lethbridge-Stewart had a space-time telegraph unit to contact the Doctor. Maybe he updated that, and someone kept the number when they left the organization. Churchill's descendants -- Winston could call the Doctor ... maybe one of his great grandchildren (although aren't all grandchildren great?) might have inherited a scrap of paper including the number. Items 7 & 8 allow for a previously unseen character. I don't think we'll see Amy and Rory again. At least I hope not, they had a fantastic conclusion to their character arc -- especially if one includes the unfilmed bit with Brian's grandson that Darvill narrated. Rose is rumored to be coming back, but she'll be along with Tennant, and they'll have their own way of barging into the story. Donna won't be back. Her character has such a sad ending, but it's a good place to leave her character in an imperfect universe. Marth and Sally aren't likely to return. So that leaves River. I hate to say it, but that's most likely a way to bring River into one of the episodes. I really am so tired of River. I'm Rivered-out.
That isn't a rumour, that is confirmed for the Special. However that is for the special, so unless this series bleeds into that - unlikely. Something else springs to mind - is Clara randomly selected for upload or targeted? Surely the latter?
...I'd say the chances of the woman being River depend on whether or not Clara's mystery is part of some nefarious GI masterplan or unrelated. If she's a weapon or a way to get to him then I doubt it's River. If her nature is not a threat to him, then it could well be River -- and Clara will also turn out to be one of the keys to solving whatever the big arc threat is this demi-season. I have another seeming puzzle... this would seem to be how Clara got the computer-genius skills displayed in Asylum, but if that was a future version of her why didn't she recognize the Doctor? I suggested in the review thread that she is the Eternal Companion, existing at various levels of time.
I just noticed something else. Clara snatched "Summer Falls" from the boy's grip and asked, "What chapter are you on?" "Ten," said the boy. Clara handed the book back. "Eleven's the best. You'll cry your eyes out." Alright ... Moff likes to seed references to eleven throughout his episodes. But in this case, if Clara's line refers to the Doctor as the best, why will we cry our eyes out? Something ominous is coming.
I watched The Nerdist later yesterday evening, and in his interview Matt Smith seemed to hint that everything was "leading up to the 50th." So it's quite possible that the anniversary will indeed play some part in the main season. Who knows, though? As for the girl in the shop, I don't know. Could be River, though that's too easy. Could be Sally Sparrow, which I think would be awesome (and correct me if I'm wrong, but didn't Moffat write "Blink?"). Could be Rose (she has been known to work in a shop, but she's theoretically stuck in Pete's World). Old Clara and/or some alternate version of Clara? Meh.
My guess is that Clara got the TARDIS phone number from either Vastra (in human disguise) or Jenny. What they're doing in modern day will be part of the story arc.
Yea, Vastra was my immediate thought. Hadn't considered any of the alternatives until reading them here.
Jeez, people just seem to have Rose on the brain around here. No way in hell they'll pull that trick again.
Funny if it were Donna, but my money is on River. Though, the Doctor did tell Jenny and Vastra to wait for him, so it could be another future Doctor setting things up for the past Doctor and getting Vastra or Jenny. River seems more likely. Though Susan or Victoria are distant possibilities for me. That would be a nice touch for the anniversary.