Autovivification is very handy on occasion - but can get in the way also. Seeing as the very most of the time I want the DWIM behaviour (sometimes I outright rely on it), I'd prefer this stricture to be off by default but available to whomever wants to enable it on a scope-by-scope basis (exists $key{doesnt_exist}{this_neither} comes to mind).

Makeshifts last the longest.