It's probably the only option as I don't see Apple doing any follow-on events in 2017 (I expect the iMac Pro and HomePod to ship without an event).
But with considering how much we'll probably see (new iPhones, new AppleTV, new Watch and all four OS updates), I don't know where the Mac Mini would fit in unless it's either a "One More Thing" or just an announcement that it has a slightly faster Haswell CPU ala the MacBook Air (which would mean no TB3/USB-C). And if they do that, why not have just said so at WWDC?