According to Stephen Hall, a senior editor for 9To5 Google, the Google Pixel and Pixel XL barely missed the boat on waterproofing, and the feature is "definitely coming with next Pixel device." Hall took to Twitter to assert that he had been told about the upcoming feature back in October, but had forgotten to disclose this detail to the internet. Hall did not reveal a source in his Tweet, but went on to explain exactly why the feature was cut, stating that time constraints were partly responsible, as was debate over the value proposition of the phone and its hardware features, with a great camera winning out over water resistance.
While there was method of fact-checking this information that was provided, the rumor lines up quite nicely with the reality of things; the Pixel and Pixel XL were hailed by some as rush jobs, but still managed to garner excellent reviews. The two phones were created in less than a year in total, far less than the development cycle for most phones, or even the Nexus lineup, the predecessor to the Pixels. Naturally, the camera, which Google's engineers are said to have wound up choosing to optimize over the inclusion of waterproofing, is one of the best on smartphones today. According to DXOMark it is the best smartphone camera out there right now.
Rumors thus far point to the next generation of the Pixel family of smartphones sporting a new design and a huge number of new features. While a few notable missing features from the current lineup, such as wireless charging, may not have any indication in the wild as to whether they will be on the next Pixel device, this somewhat credible rumor makes it seem quite plausible that the new device will feature some sort of protection against aquatic ingress and harm thereof. As with any rumor, regardless of the source or how logical it seems, this should be taken with a pinch of salt; Google has yet to officially unveil any details at all about the next members of the Pixel family, and will likely keep it that way for a while as it's still very early in the year.