WEC:
- at least one or two of the major rumoured programmes for the new LMP1 class to officially materialize, if at least for the second season of the new rule set.
F1:
- rookies making a positive name for themselves
- Ferrari's gamble on Leclerc paying off as handsomely as it can
- regular podiums for more than the top 3 teams
- a Ricciardo shoey even after his Renault move
- championship decided at the last race with a clean on-track battle
IMSA:
- Penske, CORE and Joest grabbing fair shares of wins against Formula Cadillac
- Zanardi's BMW winning its class at Daytona
Indycar:
- Robert Wickens recovering enough to get back into the cockpit, if poetic justice were to work - the recovery happening in time for Pocono next year
- Pagenaud or Bourdais claiming the Indy 500, at this year's 500 I was literally the only one in that grandstand section cheering for them in the driver intros 
- over-winter aero updates to enable better racing on the superspeedways
- 17 races => at least 8 different winners
- a good enough performance at the 500 by Alonso to convince him and McLaren to go full-time in 2020
Random others:
- the usual excitement for the Bathurst 12 Hour and Nurburgring 24h
- less major championships becoming foregone conclusions by July
- breakthrough season somewhere (not W Series) for any promising female driver
- Formula E to keep to its upward trend and convert at least some of its current detractors
Personal note - since in 2019 I will be planning my 2020 trips, the calendar announcements to fall together well enough so I can correctly plan trips to the 2020 Nurburgring 24h and to a MotoGP race during 2020 (most likely Brno).