Together with Nick Koston from cPanel we made big compiler progress today.
As I found out, 5.6.2 compiles flawlessly huge modules, just a few optimizations should be added, esp. sharing method name strings, "package::name".
So I enabled 5.6 also. Just getting the linker line right might be tricky from platform to platform on 5.6. ExtUtils::Embed is a nightmare on 5.6.
Some tests failed because all variables in the %main:: stash were not initialized, from the very beginning on, since 1998. We fixed that today, so two failing tests pass now, but we got another failure because on the main stash destruction there is a null pointer free. Should be easy to fix though.
It's advancing faster than I thought. Just minor bugs are still lurking somewhere.