Well, when I'm working I might be in a Word document, an IDE or something and it will be open for a few hours. In the meantime the taskbar is visible. But I just like to have it visible to switch to other apps whenever I want. But the burn-in would happen in a few months already.
I also often have external monitors connected (or multiple monitors to my PC in the future), which also means that the taskbar will be less likely to change often. If the taskbar is smart enough to apply a few color changes, it would already help. Or move pixels around. Or change brightness as well. The changes need to be minimal (so the whole process is fine if it takes a few minutes), in order to not distract but it would be helpful in making OLED displays last longer.
Of course I could set it to auto-hide but thats just not how I like to work and a short time to screensaver or something is only helpful if the computer isn't in use.