How do we know? Well, the big hint is that Blaster Master Overdrive was given a PG rating by the Classification Board on April 12. See?
Typically, if a game's rated, it gets released; and once a game's rated, it gets released very soon. Our money's on as soon as next week.
Why the big deal? Well, back on the NES, Blaster Master was an excellent mix of side-scrolling tank action (see above right) and top-down action-adventuring (see left). That NES original saw its Virtual Console release just last week, in fact. Overdrive looks to capture the same Metroidvania-before-there-was-Metroidvania vibe of the original, albeit with some spiffier visuals.
I can't wait.