When do you bet that 64-bit hardware will be common?
16-bit hardware and paging extensions lasted from the Commodore to the 386 Intel's PAE hack and lack of a visible 64-bit consumer strategy (Itanium is not a consumer strategy) suggest that they will try to put off the 64-bit migration in the same way. Given the performance and space hits you get with 64-bits, it might win.
As for memory for speed, if the amount of pre-buffering assigned to arrays, hash fill for a split of hashes, and similar parameters were tunable at runtime, then less could be made to work. Perl would still trade memory for performance, but how much could be adjusted significantly.