I'm not sure I get the motivation. Isn't Perl a Unix-y language? You can get "interop" by using pipes or other IPC.
This seems like a heavy, Java-esque solution. 50 lines of Perl does a lot, let alone 1000. Not sure I want to see 20,000 lines of mixed Perl 5 and Perl 6.
Well, the goal is to make sure that the plentiful modules on the CPAN (all in Perl 5) are usable for everybody involved. You're right, directly mixing Perl 5 and Perl 6 isn't likely to be a common usage - at least, doesn't seem that way to me.
The p2 goal is to use as much non-conflicting p6 syntax within p5, and mark conflicting parts in special lexically scoped syntax blocks.
But data and methods should be shared, the ast, compiler, vm, threads and event model ditto.
Syntax blocks also allow easier ffi and sql interaction,
{ use syntax "C"; c declarations ... } being a nice FFI language,
compared to "extern { c decls; ... }", which is also nice.
We want to use efficient signatures, methods, classes, tasks, coros, promises,
hyper operators, types, lazy lists and so in perl, regardless if you call it p5,
p6 or p2.
This seems like a heavy, Java-esque solution. 50 lines of Perl does a lot, let alone 1000. Not sure I want to see 20,000 lines of mixed Perl 5 and Perl 6.