Forcing companies to open source their software is certainly possible for some senses of the word "possible". You could go a long way in that direction just by changing the copyright law to not cover software, or to only cover software if the source code is deposited with the Library of Congress. Or you could change product liability law to declare products shipped without complete, compilable source code for their firmware to be "defective". Right now the political support for such changes isn't there, but that can change over time.

More likely we're going to go in the opposite direction, though.