Currently, mongos can create an unlimited number of outbound connections to mongod's

In cases with many (a few hundred) mongos routers a temporary slowdown causes a massive, sudden increase in connections to the mongod's.

SERVER-25027 allows limiting the number of outbound connections, but this is a manual setting requiring manual configuration and testing to determine an optimal value.

What would be more beneficial is to implement a feedback loop between mongos and mongod, where new connections are rate limited slowing or preventing the negative performance implications from additional connections.

This would hopefully prevent needing to manually set SERVER-25027 settings and reduce the overall number of connection spikes.