Anything about the Pixel 4 seems to have already leaked, but there may still be space for more on the list. Nikkei's reports suggest that in China, Google has started "trial production" on a 5 G variant of the Pixel 4 (although it could be manufactured in Vietnam).
According to the tipsters, it would still use the hoped Snapdragon 855 in the LTE models. Other functional changes are not mentioned, so if this proves accurate, don't count on getting more than faster wireless.
Whether or not at Google's October 15th conference you'll hear of a 5 G version is another thing. Sample development indicates it's still early, and contacts from Nikkei suggested Google might be planning to launch a 5 G model in spring alongside a new Pixel phone budget (the Pixel 4a?). Not that it's a lot of a rush to do that. The 5 G networks for carriers are still difficult to find, and current mobile chipsets still need battery life sacrifices.
The suspected breach has not been reported on by Google. A spring 5 G upgrade may be important, though, beyond waiting for the software to evolve. In spring 2020, all network affiliates with Google Fi (Sprint, T-Mobile and US Cellular) will have 5 G operating at some capacity. A 5 G Pixel 4 would serve as a display for those upgrades and could keep people subscribed to Fi where they would otherwise be tempted to leave for other providers.