Yes, IF everyone switch to use Live CD for banking. But, good luck convincing millions of Windows users to magically drop Windows, download a Linux LiveCD and start doing everything from there. Still, when that happens, developing a malware for Linux itself
is still far easier than writing a complicated BIOS code. Crackers want short-term profit, not long-term investment. (but writing BIOS codes aren't exactly long term either, because new updates will just obsolete the malware out)
Like what others have said, you shouldn't worry about the moon falling down the Earth, but instead start worrying about real security threats that can potentially compromise your system. Start configuring firewalls, encryption and stuffs, and leave the BIOS problem for later.