if you are given only 'Perl' and told to work on any assignment, irrespective of loc/complicated designs then what are the things which you (or rather Perl) would Not be able to do at all.

Quick answer: yes, but in that case, you wouldn't be able to do it in other languages, either. This ignores the time required to do the job. As several others have pointed out, Perl could well be too slow for certain time-critical applications.