But Google already does do this, in ways that I found surprising. After buying a long-distance bus ticket last week, which emailed a confirmation message to my Gmail address, I later went into Google Maps and found that it had highlighted the bus station on the local map and placed the time of my bus' departure beside it. I believe it does this same sort of thing with calendar events as well (both in implicitly creating calendar events based on scraping emails, and in creating map highlights based on events you've explicitly created). Convenient no doubt, but I'm not sure I want many more implicit interactions between the apps in Google's ecosystem.

EDIT: Here's another one: after taking photos using the camera app (Android phone), Google Maps later pops up a system notification asking me to upload my photos to the location page of whatever establishment I appeared to be in at the time (bar, park, nightclub, etc.). Frankly, I'm frustrated that I can't find a setting to disable these unwelcome prompts without turning off Maps notifications entirely.

EDIT 2: I suppose I should clarify that I do travel a lot, and the specific feature described in the OP--suggesting things to do based upon inferring your status as an out-of-towner--sounds very useful. But I'd definitely only want it as an opt-in feature, not opt-out.