### FEATURE REQUEST

Currently, when a bitcoin node is set up with a connection to both TOR and normal IPv4/6 internet, the 8 outbound-only connection slots, almost always get filled with nodes connecting over IP.
Adding a config option, which would try to ballance these connections based on what kind of network they go through, would be benefficial in many ways:

1. It would add edges between bitcoin network on TOR and normal internet, reducing delays, and the risks associated with an attacker isolating a part of TOR-bitcoin-network from the rest of the world
(Or an ISP/government man-in-the-middling all the normal IP connections)

2. It would help hide/annonymise normal user's transactions from his/her ISP, by mixing them with TOR-outbound ones

3. It would reduce the stress on normal general purpose TOR exit nodes, as users would more likely/reliably connect to TOR-IPv4/6 bitcoin nodes instead of exiting into normal internet first, and then connecting to default IPv4/6-only bitcoin nodes

I understand it is possible to create such bridges already, by forcing connections to TOR-only nodes, or by just running a node with lots of inbound slots, but I think the proposed option, would greatly increase the number of such relays, and remove the need for user to maintain a TOR-node whitelist, by handing this work off to normal bitcoind connection finding algorithm.

This could be implemented as a minimum number of connections for each network, or just a simple evening boolean switch. (Which could be enabled by default for bitcoind installs with TOR connectivity)

In the future, if bitcoin was to support a new network type (for example cjdns/I2P/GNUnet), this option would help establish a presence on the new network faster

bitcoind: 0.15
{
    
    
    const std::map<std::string, std::string> canonical_representations_ipv6{
        {"0000:0000:0000:0000:0000:0000:0000:0000", "::"},
        {"000:0000:000:00:0:00:000:0000", "::"},
        {"000:000:000:000:000:000:000:000", "::"},
        {"00:00:00:00:00:00:00:00", "::"},
        {"0:0:0:0:0:0:0:0", "::"},
        {"0:0:0:0:0:0:0:1", "::1"},
        {"2001:0:0:1:0:0:0:1", "2001:0:0:1::1"},
        {"2001:0db8:0:0:1:0:0:1", "2001:db8::1:0:0:1"},
        {"2001:0db8:85a3:0000:0000:8a2e:0370:7334", "2001:db8:85a3::8a2e:370:7334"},
        {"2001:0db8::0001", "2001:db8::1"},
        {"2001:0db8::0001:0000", "2001:db8::1:0"},
        {"2001:0db8::1:0:0:1", "2001:db8::1:0:0:1"},
        {"2001:db8:0000:0:1::1", "2001:db8::1:0:0:1"},
        {"2001:db8:0000:1:1:1:1:1", "2001:db8:0:1:1:1:1:1"},
        {"2001:db8:0:0:0:0:2:1", "2001:db8::2:1"},
        {"2001:db8:0:0:0::1", "2001:db8::1"},
        {"2001:db8:0:0:1:0:0:1", "2001:db8::1:0:0:1"},
        {"2001:db8:0:0:1::1", "2001:db8::1:0:0:1"},
        {"2001:DB8:0:0:1::1", "2001:db8::1:0:0:1"},