Unsurprisingly apps such as SwiftKey relied on Bing for its built-in search engine, but it seems that Microsoft could have quietly conceded that users prefer Google because in the latest version of the app, Microsoft has added Google as one of the options that users can choose from for its search engine.
This means that if you much prefer to use Google over Bing, you now have that option to choose from. At the moment there are only two options: Bing and Google, so if you prefer using a different search engine, such as DuckDuckGo, you might be out of luck. That being said, using Google on SwiftKey does bring it closer to making it similar to Gboard, Google’s own keyboard app, but if there are certain SwiftKey features that you prefer, this is now an option worth exploring.
These changes should be live in the latest version of the app, so make sure that you update it if you want to have the option of using Google in SwiftKey.