Yea, originally Jenna Louise Coleman started in The Snowmen
, and then they decided to write her into Asylum of the Daleks
and had to do some rewrites to The Snowmen.
So, I imagine, the inclusion of Oswin in Asylum of the Daleks
, led to having her die again in The Snowmen
, which prompted a rewrite to update Clara to modern Clara in Nightmare in Silver
Yeah, that's how I interepret it. It was stated back when Asylum aired that Oswin was originally meant to be a seperate, unrelated character until JLC was cast as Clara, then she became Oswin as well. The Moffat had to re-write The Snowmen.
I imagine The Bells of St. John would still have involved Clara being attacked by Spoonheads and magically getting computer knowledge. Having her be Victorian probably would have helped that story, as it would explain why she had next to no computer knowledge at the start and it would actually make the fact she suddenly made a joke about Twitter actually be something worth mentioning.
Of course, then the problem becomes why are the Victorian children going on a TARDIS trip? They couldn't go on the internet and find pictures of Clara in a haunted house in the 1970s or on a Soviet submarine in the 1980s.