It's certainly possible that Google would kill FitBit, but I have a feeling they're looking far ahead and seeing the potential in being the predominant biometrics company. Biometrics may be the next frontier in how Silicon Valley will make money from our data. Run of the mill internet data mining has been done to death, but if Google can get everyone to wear devices that will provide health data to potential buyers,…
If that's the case, it's only likely to be so for a very few years before we start seeing at least the more progressive jurisdictions like California putting severe restrictions on how that data can be used—not just "with consent", but "at all", given how easy it is for them to tack any kind of "and we get to sell all your data" clause into a user agreement.