I’ve added a section to the Istanbul Roadmap page on the Ethereum wiki proposing a security review period for proposed Core EIPs.
This means having some people do security reviews – which might mean engaging external auditors. But it also means communication around the Core EIP proposals that are effectively Last Call, but focused on security issues. Pay attention, have a look, does this impact your current or future use cases.
2019-06-21 (June 21st), this is half way between the hard deadline for proposals, and the soft deadline for major client implementations.