I would not like this. This is the kind of change that made google search so annoying. (Eg what if I want to track the history of 'self-driving' vs 'auto pilot' in sales pitches? Or more basically, what if the system wrongly interprets me wrongly?) Better to support | or similar old-fashioned search engine syntax and dwis and not dwim.

Synonym functionality is good as long as there's an easy way to disable it, either globally or by wrapping the term in quotes.