There's two types of metrics it seems, proxy.node and proxy.process. Unfortunately, in at least a few cases, the same metrics get duplicated into both. I'm not sure why that makes sense, ever, so I think we should clean that up. That would certainly make it less confusing.
Secondly, it seems proxy.node metrics, which are registered via RecordsConfig.cc, are primarily used for computed metrics. These are metrics synthesized via the stats.config.xml mechanism. Albeit being useful, what's bad with the current design here is that adding new metrics to the XML config file still requires a change to RecordsConfig.cc. This makes no sense to me, so perhaps the proxy.node metrics should all be eliminated from RecordsConfig.cc, and exclusively owned (registered and updated) via the XML config format.
Elimination, or renaming, of any of these metrics would be an incompatible change. Therefore, it would go into 6.0.0.