Yeah, I guess that'd be throwing the baby out with the bathwater. I retract.

Another possibility would be to issue a warning when attempting to remap mode-line or header-line. The user would at least see that what they're doing is fraught. I believe this would require reconciling the terminal vs GUI difference for mode-line you mentioned earlier. This would still be adding specialization in a generalized place, and arguably that's a worse place to do it than where you added it in your patch, so feel free to disregard that idea.

Thanks,

Aaron