### 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
{
    
    std::optional<CNetMessage> msg(std::move(vRecv));
    
    msg->m_command = hdr.GetCommand();
    msg->m_time = time;
    msg->m_message_size = hdr.nMessageSize;
    msg->m_raw_message_size = hdr.nMessageSize + CMessageHeader::HEADER_SIZE;
    uint256 hash = GetMessageHash();
    
    RandAddEvent(ReadLE32(hash.begin()));
    
    if (memcmp(hash.begin(), hdr.pchChecksum, CMessageHeader::CHECKSUM_SIZE) != 0) {
        LogPrint(BCLog::NET, "CHECKSUM ERROR (%s, %u bytes), expected %s was %s, peer=%d\n",
                 SanitizeString(msg->m_command), msg->m_message_size,
                 HexStr(Span<uint8_t>(hash.begin(), hash.begin() + CMessageHeader::CHECKSUM_SIZE)),
                 HexStr(hdr.pchChecksum),
                 m_node_id);
        out_err_raw_size = msg->m_raw_message_size;
        msg = std::nullopt;
    } else if (!hdr.IsCommandValid()) {
        LogPrint(BCLog::NET, "HEADER ERROR - COMMAND (%s, %u bytes), peer=%d\n",
                 hdr.GetCommand(), msg->m_message_size, m_node_id);
        out_err_raw_size = msg->m_raw_message_size;
        msg.reset();
    }
    
    Reset();
    return msg;