Its happened before and I recon Photoshop is pretty close.

Here are some trademarks that become public domain Aspirin, Xerox, Kleenex, Q-Tips. The only reason Photoshop has retained its trademark is because adobe makes significant effort to police their rights to it. This means that adobe doesn't want you to call editing a photo photoshoping as that opens the door for it to become a common term and thus in the public domain.

Tldr: if we continue to use the word "Photoshop" in a generic sense then it will eventually force it into pubic domain regardless of adobes desires.