Alot of people think of the "clinch" in terms of a skilled fighter either someone who knows Muay Thai, or a greco-roman wrestler. If you watch two unskilled people go at it, they will clinch up just like boxers do. So I think it would be stand to reason if katas include techniques against other kinds of grabs and attacks that they would have had answers to an opponent that clinches.
I know I'm probably preaching to the choir, but katas are not set in stone. They illustrate certain concepts and principles and use techniques to show them, but they do not contain ALL the various options that can be understood. For example as I'm drawing my right hand back to the left hip (cup and saucer position found in many katas) I can do a rake across the eyes or an ear slap as I bring it across. Is it explicitly spelled out as such? No, it is understood that once a person got to that point they would understand certain things from their basics and other exercises.
Back to kicking. If I step forward, what am I doing? Am I gaining position on a close attacker? Am I closing the distance on an attacker? If we use the premise that all of our kicks are exagerrated steps, than it is easy to insert those concepts into the katas without changing it.