The point is that once they are no longer compatible, people would standardize on the one that they're familiar with which is most likely the one that's running on their machine.

There are enough pretty annoying and long standing terraform issues that if opentofu started picking them off I'd consider switching.

You can kinda see this with vim and neovim where both are continuing to exist and benefit each other.

Encrypted state files are either done or coming soon. That's going to be a big one, since Hashicorp used that as a selling point for Terraform Cloud.

But currently, people are equally comfortable with both; the CLI commands are exactly identical between the two, save for the name of the binary itself. In any org where both are in use, if people are forced to choose at some point, they will have to balance many other factors besides familiarity, such as features and confidence in the platform.