When both players facswitch to another land factory:

lol

But wait, is it actually consensus that switching to ravens/thunderbird/owl (maybe athenas or krow/gunships also included here?) is always the most cost-effective use of a second fac in 1v1?

Most players make gunships or airplanes as a second factory in 1v1.
I think gunships are more common than airplanes, but personally, I think that airplanes are the superior option.

Airplanes and gunships arguably have the most different units from land factories and will in most cases force the enemy to make dedicated anti-air units while some additional land units from another factory can generally can be countered what is already on the field.