It is worth reminding that in the past, serious initiatives for coordinated monetary policy have been taken under the 1985 Plaza Accord and the 1987 Louvre Accord in order to stabilise the dollar exchange rate.
If things move towards such a policy coordination, it should in my view take the following form: i) the Fed could perhaps extend a new swap line to the central banks of EMEs, like the swap lines it offered at the start of the global crisis (a kind of formal policy coordination), and/or ii) a commitment on the part of the four major central banks to communicate their monetary policies in a clear and timely manner within the context of their forward guidance policies, as was agreed in a G20 Meeting in 2014, (a kind of informal policy coordination, whereby major CBs are mindful of the consequences of their actions).