Disrupting Wall St. implies not just making a "new" UI/UX/Interface for banking clients (like Mint or Square), it implies looking at changing the Banks inherent Business Model. Can Silicon Valley pull it off? Well, from a foreigners perspective (commenting from Lisbon, Portugal) Silicon Valley has a very engineer centric perspective on problem solving, and while engineering inputs may be useful, this is not an engine…
So one way to disrupt banks would be to put these resources in the hands of an individual.
Social Networking might be a good research direction to solving the P2P information problem solving, by revealing our preferences.
I heard or read somewhere that much of the lending for small businesses and startups happened through one's personal network. Here may be an excellent opportunity for Facebook. This is also an area where the information asymmetry is often reversed. (For example: Your crazy uncle Zeb might look a good credit risk to the bank, even though you know it's all because your aunt was managing the money until she ran off to Belize with the plumber last year.)