From my perspective I don't want it to be a plain default. I use Perl on the command line a great deal and having to type "my" and such "just because" would be a small burden but one that would add up quickly to be extremely irritating; irritating to the point of exploring other languages to see if they were less of a hassle. There may be some middle ground where -e turns off strict or any scope change turns it on or something(?).
What haukex said about use {version} and backwards compatibility is germane I think.