The biggest bit I miss from messing with proxies in the past has been "stop, hold, upgrade" game that web-servers could play with proxies.

This means that you can have your proxy "hold requests" for a few seconds while your system restarts in the background & slowly let off the requests out to the backend in "one more request per second" scale up.

This sort of stuff would work great with a proxy that actually understands something a kubernetes scheduler & know when a node is failing/restarting etc.