Not a chance. With the recent announcement of subscription based, Adobe already upsets its loyal users; therefore, open-source Fireworks only providers customers a chance to leave the Adobe universe quicker.
Photoshop and Illustrator are the major tools for web designers even though they both are capable of doing things way beyond the web. Fireworks combines the two, but focuses specifically for the web. Fireworks is probably all that is needed for most web designers if they don’t have the luxury of using Photoshop and Illustrator.
As a result, Adobe isn’t going to open-source Fireworks to compete against it own products. Just my two cents, but I hope I am wrong.