I'd see a Cars GP possible. With a mechanic career (I feel like there are not enough careers using the handiness skill), worn-out clothes and some other 'wheely' stuff. Ofc, it'd have motorcycles in addition to cars. And maybe a small world looking like industrial suburbs.
And they could use some of the silly naming conventions from the last EPs - something like 'Discover motors' or Get wheels'.
Plus it'd allow those who're not fond of cars in TS4 to opt out of them by not buying the pack.
Another supernatural pack is likely, though it might take a while - and I wouldn't be against another travel pack.