Well, maybe at an API and prompt level. But if Google pull ahead in this space then you may become dependent on what it alone can do functionally. Even if you can trivially switch LLM and prompt, if the others aren't able to do something equivalent (or at the same level of quality) then you're still locked in. Until now we've basically had this situation with OpenAI.
Et viola, your application is now free from LLM lock-in.