Partner visa changes requiring sponsorship approval before a visa application is lodged will NOT be commencing 17 April 2019.
The separate sponsorship framework will first be implemented in the new Sponsored Parent (Temporary) visa which will be open for sponsorship applications from 17 April 2019.
Further regulation and system changes are required for the new framework to apply to other visas. At this stage, there is no timeframe for expansion of the new sponsorship framework to other family visas and therefore the current arrangements for existing visas, including partner visas, will continue to operate from 17 April 2019.
Guess that the online system is not ready yet.
BUT... beware and be prepared...big changes are coming up.