...

• Be able to lock Solr's memory to prevent swapping (SOLR-14335)
• Change/rename some Sysprops (like jetty.port → port)
• Be able to shutdown JVM in various error situations (SOLR-6935 etc)
• Easier to control things like CORS in our own config (SOLR-12292)
• Get rid of web.xml and instead build our contexts and paths from Java code, driven by Solr config
• Get rid of jetty-ssl.xml and instead control SSL config in Java code, driven by Solr config
• Slim down bin/solr & bin\solr.cmd and move more startup logic into our bootstrap Java code
• Unified handling of key timeout values (SOLR-13457)

Compatibility, Deprecation, and Migration Plan

...