It looks like Sony are taking a leaf out of the Fuji playbook by introducing new substantial features through firmware updates rather than entirely new bodies. The Sony A9, A7RIII and A7III are about to get quite a significant feature upgrade with new firmware updates coming out over the next few months.
The first firmware update for the Sony A9 is due in March bringing the realtime Eye AF performance expected in the newly announced Sony A6400. The Sony A9 will see Animal Eye AF added in a second update coming in summer. The A7RIII and A7III will also receive these updates in a single firmware in April.