Bank deposits are financial assets- which gets its value from a contractual right or ownership claim.
When you deposit money in a bank, they lend that money out, they make a return, and in a sane world you would receive interest on that money.
Using this definition of a financial asset, I don't think bitcoin qualifies, it is more of an intangible. It might be a financial asset only if it is held at a custodian.
Congress and the courts decide what a security is, not the SEC. The SEC is the enforcement agency from what I can tell.