It took 1 day to integrate SOCKS5 for [outbound] and [manual] (p2p) connections. These are configured independently (and there is no inbound p2p or incoming service endpoint support).
[outbound]
socks = localhost:1080
username = foo
password = bar
[manual]
socks = localhost:1080
username =
password =
Credentials settings are parsed, but password authentication is not hooked up yet. I'll get that in the morning. This is the very first successful round trip message via socks5 proxy, and the very first block synced (later in the same connection).