The first part of the "Orderer V3 RFC" calls for the removal of deprecated components:

• Kafka
• Solo
• System channel support

See RFC:

• https://hyperledger.github.io/fabric-rfcs/text/orderer-v3.html
• Ordering service framework fabric-rfcs#50

In addition, since block gossip is deprecated since v2.5, change the defaults accordingly, e.g. see #3961 , making it disabled by default, even if respective parameters are missing.