Create a staging environment within Core

[carike]

A lack of trust and fear of things breaking seems to be the reason why a lot of people do not update their WordPress Core installation or plugins.

It seems like a built-in staging environment (along with the ability to roll back) can go a long way towards improving the adoption of auto-updates without alienating stakeholders.

It seems like a possible way to do this may be to create a staging site (sharing the DB by default, but with the possibility of separate DBs via a constant) under a subfolder.