It could be the year Main Street's appetite for cryptocurrency exposure meaningfully grows.Although it's been two years since the first spot bitcoin ETFs began trading on U.S. exchanges, BlackRock's Jay Jacobs thinks they're a fairly new concept."It's still so early," the firm's U.S. head of equity ETFs told CNBC's "ETF Edge" this week. "Many investors have still just been starting their educational journey around what is bitcoin, [and] how might it fit in a portfolio .… We see this still being very early d ...