I'm exploring whether or not the implementation of Perl would become simpler if there was one datatype used to represent the things we see as strings, lists, and hashes.
It might be simpler, but it would never happen. You seem to view this as just a "matter of time" since computers will be so fast they will make up for the "inefficiency" of this LISP-y implementation. The speed of a computer is a factor, but it is probably the least important factor when it comes to "efficiency."
Constant speedups are one thing, but if you have a bad algorithm (like blindly searching a list to implement an associative array), the problem will scale poorly no matter how fast your computer is. The only way a futuristic computer running a linear-time algorithm could keep up with another computer running a constant-time algorithm would be if it could somehow compress time.
If I had to choose between a fast computer and fast algorithms, I'd choose fast algorithms ;)
You'd have a better chance of convincing me that this is a good idea if the implementation stays efficient and the everything-is-a-list is just a unifying interface to whatever the underlying structure is. Although I still don't see what this does that LISP doesn't already do.