One of the main reasons given for Apple’s decision to limit most discussion about future products is not to harm sales of existing hardware. This is certainly true for incremental product updates. So if you knew what was coming in the 2020 iPhone, you might postpone buying the current (2019) model. Well, at least when the next version is coming soon.
More or less.
But when it comes to an iPhone, Apple has been quite predictable in releasing annual updates, and for the most part, the new model isn’t so improved compared to the current model that you should rush to upgrade. At this point, most iPhone owners probably know that new models are forthcoming — and when — and they will decide if they need to wait for something special, or just buy what they want now.