The deeper issue that always comes up is that tail-recursion would make caller give very different results. Which is a lot of fun when you are trying to debug a complex call. (Carp depends on caller for its output.)

Another subtle change is different destruction mechanics. In order to do tail-recursion, you have to clean-up your current variables, etc. With reliable destruction mechanics, this may cause interesting surprises. For instance consider the technique at •Re: sub and anonymous sub. Or consider ReleaseAction. Their behaviour changes. It already changes with goto, but at least there is an easily explained cause for the change. If it is done behind the programmer's back, how do you address the confusion?

I should also note that writing recursive routines that automatically perform iteratively makes more sense in Scheme where function calls are very cheap. When they are relatively expensive (as they are in Perl), the coolness isn't quite as compelling...