Just as an update, Brad Fitzpatrick seems to be working on Perl on AppEngine. It seems that Google wants/needs to create a hardened/Safe/crippled version of Perl that is statically linked and can't load XS modules, which might take some time/effort. On the upside, Postgres already seems to have such an embedded Perl interpreter, so it might be not too much work to create a comparable embeddable static Perl.
Brad and Artur Bergman have pushed out Sys::Protect, which disables some Perl opcodes, which looks like a first step to disallowing system interaction.
